| 1207 | Unique Number of Occurrences | Solution | O(n) | O(1) | | Easy | |
| 1160 | Find Words That Can Be Formed by Characters | Solution | O(n) | O(m) | | Easy | |
| 1154 | Day of the Year | Solution | O(1) | O(1) | | Easy | |
| 1137 | N-th Tribonacci Number | Solution | O(n) | O(n) | | Easy | |
| 1122 | Relative Sort Array | Solution | O(n) | O(n) | | Easy | |
| 1089 | Duplicate Zeros | Solution | O(n^2) | O(1) | | Easy | |
| 1079 | Letter Tile Possibilities | Solution | O(1) | O(1) | | Medium | |
| 1078 | Occurrences After Bigram | Solution | O(n) | O(1) | | Easy | |
| 1071 | Greatest Common Divisor of Strings | Solution | O(m*n) | O(1) | | Easy | |
| 1065 | Index Pairs of a String | Solution | O(nlogn) | O(1) | | Medium | |
| 1056 | Confusing Number | Solution | O(n) | O(1) | | Easy | |
| 1055 | Fixed Point | Solution | O(n) | O(1) | | Easy | |
| 1051 | Height Checker | Solution | O(nlogn) | O(1) | | Easy | |
| 1047 | Remove All Adjacent Duplicates In String | Solution | O(n) | O(1) | | Easy | |
| 1043 | Partition Array for Maximum Sum | Solution | O(nk) | O(n) | | Medium | DP |
| 1038 | Binary Search Tree to Greater Sum Tree | Solution | O(n) | O(n) | | Medium | DFS, tree |
| 1037 | Valid Boomerang | Solution | O(1) | O(1) | | Easy | Math |
| 1033 | Moving Stones Until Consecutive | Solution | O(1) | O(1) | | Easy | Math |
| 1030 | Matrix Cells in Distance Order | Solution | O(R*C) | O(1) | | Easy | |
| 1029 | Two City Scheduling | Solution | O(nlogn) | O(1) | | Easy | |
| 1022 | Sum of Root To Leaf Binary Numbers | Solution | O(n) | O(n) | | Easy | |
| 1021 | Remove Outermost Parentheses | Solution | O(n) | O(n) | | Easy | |
| 1020 | Number of Enclaves | Solution | O(mn) | O(mn) | | Medium | Graph, DFS, BFS, recursion |
| 1018 | Binary Prefix Divisible By 5 | Solution | O(n) | O(1) | | Easy | |
| 1014 | Best Sightseeing Pair | Solution | O(n) | O(1) | | Medium | |
| 1013 | Partition Array Into Three Parts With Equal Sum | Solution | O(n) | O(1) | | Easy | |
| 1011 | Capacity To Ship Packages Within D Days | Solution | O(nlogn) | O(1) | | Medium | Binary Search |
| 1010 | Pairs of Songs With Total Durations Divisible by 60 | Solution | O(n) | O(1) | | Easy | |
| 1009 | Complement of Base 10 Integer | Solution | O(n) | O(1) | | Easy | |
| 1008 | Construct Binary Search Tree from Preorder Traversal | Solution | O(n) | O(1) | | Medium | Recursion |
| 1003 | Check If Word Is Valid After Substitutions | Solution | O(n) | O(n) | | Medium | |
| 1002 | Find Common Characters | Solution | O(n) | O(1) | | Easy | |
| 999 | Available Captures for Rook | Solution | O(1) | O(1) | | Easy | |
| 997 | Find the Town Judge | Solution | O(n) | O(n) | | Easy | |
| 994 | Rotting Oranges | Solution | O(m2n*2) | O(m*n) | | Easy | BFS |
| 993 | Cousins in Binary Tree | Solution | O(n) | O(m) (m is length of the nodes that has the max number of nodes on the same level) | | Easy | Tree, BFS |
| 989 | Add to Array-Form of Integer | Solution | O(max(N, logk)) | O(max(N, logk)) | | Easy | Array |
| 987 | Vertical Order Traversal of a Binary Tree | Solution | O(n) | O(n) | | Medium | Recursion |
| 985 | Sum of Even Numbers After Queries | Solution | O(n) | O(n) | | Easy | Array |
| 979 | Distribute Coins in Binary Tree | Solution | O(n) | O(1) | | Medium | Recursion |
| 977 | Squares of a Sorted Array | Solution | O(nlogn) | O(1) | | Easy | Array |
| 976 | Largest Perimeter Triangle | Solution | O(nlogn) | O(1) | | Easy | Math Array |
| 974 | Subarray Sums Divisible by K | Solution | O(n) | O(n) | | Medium | Array |
| 973 | K Closest Points to Origin | Solution | O(nlogn) | O(K) | | Easy | Math Sort |
| 970 | Powerful Integers | Solution | O(?) | O(1) | | Easy | Math |
| 966 | Vowel Spellchecker | Solution | O(hlogn) | O(n) | | Medium | Hash Table, String |
| 965 | Univalued Binary Tree | Solution | O(n) | O(h) | | Easy | DFS, recursion |
| 961 | N-Repeated Element in Size 2N Array | Solution | O(n) | O(1) | | Easy | |
| 953 | Verifying an Alien Dictionary | Solution | O(1) | O(1) | | Easy | |
| 951 | Flip Equivalent Binary Trees | Solution | O(n) | O(h) | | Medium | Tree, DFS, recursion |
| 950 | Reveal Cards In Increasing Order | Solution | O(nlogn) | O(n) | | Medium | |
| 944 | Delete Columns to Make Sorted | Solution | O(n) | O(1) | | Easy | |
| 942 | DI String Match | Solution | O(n) | O(n) | | Easy | |
| 941 | Valid Mountain Array | Solution | O(n) | O(1) | | Easy | |
| 938 | Range Sum of BST | Solution | O(n) | O(n) | | Medium | BST, recursion, DFS |
| 937 | Reorder Log Files | Solution | O(n) | O(n) | | Easy | |
| 935 | Knight Dialer | Solution | O(n) | O(1) | | Medium | |
| 933 | Number of Recent Calls | Solution | O(n) | O(n) | | Easy | |
| 929 | Unique Email Addresses | Solution | O(n) | O(n) | | Easy | |
| 925 | Long Pressed Name | Solution | O(n) | O(1) | | Easy | |
| 922 | Sort Array By Parity II | Solution | O(n) | O(1) | | Easy | |
| 917 | Reverse Only Letters | Solution | O(n) | O(n) | | Easy | |
| 914 | X of a Kind in a Deck of Cards | Solution | O(n) | O(n) | | Easy | |
| 912 | Sort an Array | Solution | O(nlogn) | O(1) | | Easy | |
| 908 | Smallest Range I | Solution | O(n) | O(1) | | Easy | |
| 900 | RLE Iterator | Solution | O(n) | O(1) | | Medium | |
| 897 | Increasing Order Search Tree | Solution | O(n) | O(n) | | Easy | DFS, recursion |
| 896 | Monotonic Array | Solution | O(n) | O(1) | | Easy | |
| 890 | Find and Replace Pattern | Solution | O(n) | O(1) | | Medium | |
| 888 | Fair Candy Swap | Solution | O(n) | O(1) | | Easy | |
| 884 | Uncommon Words from Two Sentences | Solution | O(n) | O(k) | | Easy | |
| 876 | Middle of the Linked List | Solution | O(n) | O(1) | | Easy | |
| 872 | Leaf-Similar Trees | Solution | O(n) | O(h) | | Easy | DFS, recursion |
| 868 | Binary Gap | Solution | O(n) | O(n) | | Easy | |
| 867 | Transpose Matrix | Solution | O(r*c) | O(r*c) | | Easy | |
| 860 | Lemonade Change | Solution | O(n) | O(1) | | Easy | |
| 859 | Buddy Strings | Solution | O(n) | O(n) | | Easy | |
| 852 | Peak Index in a Mountain Array | Solution | O(n) | O(1) | | Easy | |
| 849 | Maximize Distance to Closest Person | Solution | O(n^2) | O(1) | | Easy | |
| 844 | Backspace String Compare | Solution | O(n) | O(1) | | Easy | |
| 840 | Magic Squares In Grid | Solution | O(1) | O(1) | | Easy | |
| 832 | Flipping an Image | Solution | O(n) | O(1) | | Easy | |
| 830 | Positions of Large Groups | Solution | O(n) | O(n) | | Easy | |
| 824 | Goat Latin | Solution | O(n) | O(1) | | Easy | |
| 821 | Shortest Distance to a Character | Solution | O(n) | O(k) (k is the number of char C in S) | | Easy | |
| 819 | Most Common Word | Solution | O(m+n) | O(n) | | Easy | HashMap |
| 814 | Binary Tree Pruning | Solution | O(n) | O(n) | | Medium | recursion, DFS |
| 811 | Subdomain Visit Count | Solution | O(n) | O(n) | | Easy | HashMap |
| 806 | Number of Lines To Write String | Solution | O(n) | O(1) | | Easy | |
| 804 | Unique Morse Code Words | Solution | O(S) | O(S) | | Easy | |
| 800 | Similar RGB Color | Solution | O(1) | O(1) | | Easy | |
| 799 | Champagne Tower | Solution | O(r^2) or O(1) | O(r^2) or O(1) | | Medium | |
| 796 | Rotate String | Solution | O(n) | O(1) | | Easy | |
| 791 | Custom Sort String | Solution | O(n+m) | O(1) | | Medium | |
| 789 | Escape The Ghosts | Solution | O(n) | O(1) | | Medium | Math |
| 788 | Rotated Digits | Solution | O(n*m) | O(1) | | Easy | |
| 784 | Letter Case Permutation | Solution | O(n*2^n) | O(n*2^n) | | Easy | |
| 783 | Minimum Distance Between BST Nodes | Solution | O(n) | O(h) | | Easy | |
| 779 | K-th Symbol in Grammar | Solution | O(logn) | O(1) | | Medium | |
| 776 | Split BST | Solution | O(n) | O(n) | | Medium | Recursion |
| 771 | Jewels and Stones | Solution | O(n) | O(m) | | Easy | |
| 769 | Max Chunks To Make Sorted | Solution | O(n) | O(1) | | Medium | Array |
| 767 | Reorganize String | Solution | O(klogk) k is the number of unique characters in given String | O(k) | | Medium | |
| 766 | Toeplitz Matrix | Solution | O(m*n) | O(1) | | Easy | |
| 765 | Couples Holding Hands | Solution | O(n^2) | O(1) | | Hard | |
| 764 | Largest Plus Sign | Solution | O(n^2) | O(n^2) | | Medium | DP |
| 763 | Partition Labels | Solution | O(n) | O(1) | | Medium | |
| 762 | Prime Number of Set Bits in Binary Representation | Solution | O(n) | O(1) | | Easy | |
| 760 | Find Anagram Mappings | Solution | O(n^2) | O(1) | | Easy | |
| 758 | Bold Words in String | Solution | O(n*k) | O(n | | Easy | |
| 756 | Pyramid Transition Matrix | Solution | O(?) | O(?) | | Medium | Backtracking |
| 755 | Pour Water | Solution | O(V*N) | O(1) | | Medium | Array |
| 754 | Reach a Number | Solution | O(n) | O(1) | | Medium | Math |
| 750 | Number Of Corner Rectangles | Solution | O((m*n)^2) | O(1) | | Medium | |
| 748 | Shortest Completing Word | Solution | O(n) | O(1) | | Easy | |
| 747 | Largest Number Greater Than Twice of Others | Solution | O(n) | O(1) | | Easy | |
| 746 | Min Cost Climbing Stairs | Solution | O(n) | O(1) | | Easy | |
| 744 | Find Smallest Letter Greater Than Target | Solution | O(logn) | O(1) | | Easy | |
| 743 | Network Delay Time | Solution | O(n^2 + e) | O(n^2) | | Medium | Graph, Djikstra |
| 740 | Delete and Earn | Solution | O(n) | O(n) | | Medium | |
| 739 | Daily Temperatures | Solution | O(n^2) | O(1) | | Medium | |
| 738 | Monotone Increasing Digits | Solution | O(n) | O(1) | | Medium | |
| 737 | Sentence Similarity II | Solution | O(nlogk + k) n is the length of max(words1, words2), k is the length of pairs | O(k) | | Medium | Union Find |
| 735 | Asteroid Collision | Solution | O(n) | O(n) | | Medium | Stack |
| 734 | Sentence Similarity | Solution | O(n*k) | O(1) | | Easy | HashTable |
| 733 | Flood Fill | Solution | O(m*n) | O(m*n) | | Easy | BFS, DFS |
| 729 | My Calendar I | Solution | O(n) | O(n) | | Medium | |
| 728 | Self Dividing Numbers | Solution | O(n*k) k is the average number of digits of each number in the given array | O(1) | | Easy | |
| 727 | Minimum Window Subsequence | Solution | O(m*n) | O(m*n) | | Hard | DP |
| 725 | Split Linked List in Parts | Solution | O(n+k) | O(k) | | Medium | LinkedList |
| 724 | Find Pivot Index | Solution | O(n) | O(1) | | Easy | Array |
| 723 | Candy Crush | Solution | O((r*c)^2) | O((r*c)) | | Medium | Array, Two Pointers |
| 721 | Accounts Merge | Solution | | | | Medium | DFS, Union Find |
| 720 | Longest Word in Dictionary | Solution | O(∑wi) where wi is the length of words[i] | O(∑wi) where wi is the length of words[i] | | Easy | Trie |
| 719 | Find K-th Smallest Pair Distance | Solution | O(nlogw + nlogn) | O(1) | | Hard | Binary Search |
| 718 | Maximum Length of Repeated Subarray | Solution | O(m*n) | O(m*n) | | Medium | DP |
| 717 | 1-bit and 2-bit Characters | Solution | O(n) | O(1) | | Easy | |
| 716 | Max Stack | Solution | O(logn) | O(n) | | Hard | Design |
| 714 | Best Time to Buy and Sell Stock with Transaction Fee | Solution | O(n) | O(1) | | Medium | DP |
| 713 | Subarray Product Less Than K | Solution | O(n) | O(1) | | Medium | |
| 712 | Minimum ASCII Delete Sum for Two Strings | Solution | O(m*n) | O(m*n) | | Medium | DP |
| 709 | To Lower Case | Solution | O(n) | O(1) | | Easy | String |
| 706 | Design HashMap | Solution | O(n) | O(n) | | Easy | Design |
| 705 | Design HashSet | Solution | O(1) | O(n) | | Easy | Design |
| 704 | Binary Search | Solution | O(logn) | O(1) | | Easy | Binary Search |
| 703 | Kth Largest Element in a Stream | Solution | O(logn) | O(n) | | Easy | |
| 701 | Insert into a Binary Search Tree | Solution | O(n) | O(h) | | Medium | DFS, recursion |
| 700 | Search in a Binary Search Tree | Solution | O(n) | O(h) | | Easy | recusion, dfs |
| 699 | Falling Squares | Solution | O(n^2) | O(n) | | Hard | Segment Tree |
| 698 | Partition to K Equal Sum Subsets | Solution | O(n*(2^n)) | O(2^n) | | Medium | Backtracking |
| 697 | Degree of an Array | Solution | O(n) | O(n) | | Easy | |
| 696 | Count Binary Substrings | Solution | O(n) | O(n) | | Easy | |
| 695 | Max Area of Island | Solution | O(m*n) | O(1) | | Easy | DFS |
| 694 | Number of Distinct Islands | Solution | O(m*n) | O(1) | | Medium | DFS |
| 693 | Binary Number with Alternating Bits | Solution | O(n) | O(1) | | Easy | |
| 692 | Top K Frequent Words | Solution | O(nlogk) | O(n) | | Medium | |
| 691 | Stickers to Spell Word | Solution | O(?) | O(?) | | Hard | DP |
| 690 | Employee Importance | Solution | O(n) | O(h) | | Easy | DFS |
| 689 | Maximum Sum of 3 Non-Overlapping Subarrays | Solution | O(n) | O(n) | | Hard | DP |
| 688 | Knight Probability in Chessboard | Solution | O(n^2) | O(n^2) | | Medium | DP |
| 687 | Longest Univalue Path | Solution | O(n) | O(h) | | Easy | DFS |
| 686 | Repeated String Match | Solution | O(n*(m+n)) | O(m+n) | | Easy | |
| 685 | Redundant Connection II | Solution | O(n) | O(n) | | Hard | Union Find |
| 684 | Redundant Connection | Solution | O(n) | O(n) | | Medium | Union Find |
| 683 | K Empty Slots | Solution | O(n) | O(n) | | Hard | |
| 682 | Baseball Game | Solution | O(n) | O(1) | | Easy | |
| 681 | Next Closest Time | Solution | O(1) | O(1) | | Medium | |
| 680 | Valid Palindrome II | Solution | O(n) | O(1) | | Easy | String |
| 679 | 24 Game | Solution | O(1) (Upper bound 9216) | O(1) | | Hard | Recursion |
| 678 | Valid Parenthesis String | Solution | O(n) | O(1) | | Medium | Recursion, Greedy |
| 677 | Map Sum Pairs | Solution | O(n) | O(n) | | Medium | HashMap |
| 676 | Implement Magic Dictionary | Solution | O(n^2) | O(n) | | Medium | |
| 675 | Cut Off Trees for Golf Event | Solution | O((m*n)^2) | O(m*n) | | Hard | BFS |
| 674 | Longest Continuous Increasing Subsequence | Solution | O(n^2) | O(1) | | Easy | |
| 673 | Number of Longest Increasing Subsequence | Solution | O(n^2) | O(n) | | Medium | DP |
| 672 | Bulb Switcher II | Solution | O(1) | O(1) | | Medium | Math |
| 671 | Second Minimum Node In a Binary Tree | Solution | O(n) | O(n) | | Easy | Tree, DFS |
| 670 | Maximum Swap | Solution | O(n^2) | O(1) | | Medium | String |
| 669 | Trim a Binary Search Tree | Solution | O(n) | O(1) | | Easy | Tree, DFS |
| 668 | Kth Smallest Number in Multiplication Table | Solution | O(logm*n) | O(1) | | Hard | Binary Search |
| 667 | Beautiful Arrangement II | Solution | O(n) | O(1) | | Medium | Array |
| 666 | Path Sum IV | Solution | O(1) | O(1) | | Medium | Tree, DFS |
| 665 | Non-decreasing Array | Solution | O(n) | O(n) | | Easy | |
| 664 | Strange Printer | Solution | O(n^3) | O(n^2) | | Hard | DP |
| 663 | Equal Tree Partition | Solution | O(n) | O(n) | | Medium | Tree |
| 662 | Maximum Width of Binary Tree | Solution | O(n) | O(k) | | Medium | BFS, DFS |
| 661 | Image Smoother | Solution | O(m*n) | O(1) | | Easy | Array |
| 660 | Remove 9 | Solution | O(n) | O(1) | | Hard | Math |
| 659 | Split Array into Consecutive Subsequences | Solution | O(n) | O(n) | | Medium | HashMap |
| 658 | Find K Closest Elements | Solution | O(n) | O(1) | | Medium | |
| 657 | Judge Route Circle | Solution | O(n) | O(1) | | Easy | |
| 656 | Coin Path | Solution | O(n*B) | O(n) | | Hard | DP |
| 655 | Print Binary Tree | Solution | O(h*2^h) | O(h*2^h) | | Medium | Recursion |
| 654 | Maximum Binary Tree | Solution | O(n) | O(n) | | Medium | Tree |
| 653 | Two Sum IV - Input is a BST | Solution | | | | Easy | Tree |
| 652 | Find Duplicate Subtrees | Solution | O(n) | O(n) | | Medium | Tree |
| 651 | 4 Keys Keyboard | Solution | O(n^2) | O(n) | | Medium | DP |
| 650 | 2 Keys Keyboard | Solution | O(n^2) | O(n) | | Medium | DP |
| 649 | Dota2 Senate | Solution | O(n) | O(n) | | Medium | Greedy |
| 648 | Replace Words | Solution | O(n) | O(n) | | Medium | Trie |
| 647 | Palindromic Substrings | Solution | O(n^2) | O(1) | | Medium | DP |
| 646 | Maximum Length of Pair Chain | Solution | O(nlogn) | O(1) | | Medium | DP, Greedy |
| 645 | Set Mismatch | Solution | O(nlogn) | O(1) | | Easy | |
| 644 | Maximum Average Subarray II | Solution | | O(1) | | Hard | Binary Search |
| 643 | Maximum Average Subarray I | Solution | O(n) | O(1) | | Easy | |
| 642 | Design Search Autocomplete System | Solution | O(n) | O(n) | | Hard | Design |
| 640 | Solve the Equation | Solution | O(n) | O(n) | | Medium | |
| 639 | Decode Ways II | Solution | O(n) | O(n) | | Hard | DP |
| 638 | Shopping Offers | Solution | O(2^n) | O(n) | | Medium | DP, DFS |
| 637 | Average of Levels in Binary Tree | Solution | O(n) | O(1) | | Easy | |
| 636 | Exclusive Time of Functions | Solution | O(n) | O(n/2) | | Medium | Stack |
| 635 | Design Log Storage System | Solution | O(n) | O(n) | | Medium | Design |
| 634 | Find the Derangement of An Array | Solution | O(n) | O(1) | | Medium | Math |
| 633 | Sum of Square Numbers | Solution | O(logn) | O(1) | | Easy | Binary Search |
| 632 | Smallest Range | Solution | O(n*logk) | O(k) | | Hard | Heap |
| 631 | Design Excel Sum Formula | Solution | | | | Hard | Design, Topological Sort |
| 630 | Course Schedule III | Solution | O(n*logn) | O(n) | | Hard | Heap, Greedy |
| 629 | K Inverse Pairs Array | Solution | O(n*k) | O(n*k) | | Hard | DP |
| 628 | Maximum Product of Three Numbers | Solution | O(nlogn) | O(1) | | Easy | |
| 625 | Minimum Factorization | Solution | O(?) | O(?) | | Medium | |
| 624 | Maximum Distance in Arrays | Solution | O(nlogn) | O(1) | | Easy | Sort, Array |
| 623 | Add One Row to Tree | Solution | O(n) | O(h) | | Medium | Tree |
| 621 | Task Scheduler | Solution | O(n) | O(26) | | Medium | Greedy, Queue |
| 617 | Merge Two Binary Trees | Solution | O(n) | O(h) | | Easy | Tree, Recursion |
| 616 | Add Bold Tag in String | Solution | O(n*k) (n is length of string, k is size of dict) | O(n) | | Medium | String |
| 611 | Valid Triangle Number | Solution | O(n^2logn) | O(logn) | | Medium | Binary Search |
| 609 | Find Duplicate File in System | Solution | O(n*x) (x is the average length of each string) | O(n*x) | | Medium | HashMap |
| 606 | Construct String from Binary Tree | Solution | O(n) | O(n) | | Easy | Tree, Recursion |
| 605 | Can Place Flowers | Solution | O(n) | O(1) | | Easy | Array |
| 604 | Design Compressed String Iterator | Solution | O(n) | O(n) | | Easy | Design, String |
| 600 | Non-negative Integers without Consecutive Ones | Solution | O(log2(max_int) = 32) | O(log2(max_int) = 32) | | Hard | Bit Manipulation, DP |
| 599 | Minimum Index Sum of Two Lists | Solution | O(max(m,n)) | O(max(m,n)) | | Easy | HashMap |
| 598 | Range Addition II | Solution | O(x) (x is the number of operations) | O(1) | | Easy | |
| 594 | Longest Harmonious Subsequence | Solution | O(n) | O(n) | | Easy | Array, HashMap |
| 593 | Valid Square | Solution | O(1) | O(1) | | Medium | Math |
| 592 | Fraction Addition and Subtraction | Solution | O(nlogx) | O(n) | | Medium | Math |
| 591 | Tag Validator | Solution | O(n) | O(n) | | Hard | Stack, String |
| 590 | N-ary Tree Postorder Traversal | Solution | O(n) | O(n) | | Easy | DFS, recursion |
| 589 | N-ary Tree Preorder Traversal | Solution | O(n) | O(n) | | Easy | DFS, recursion |
| 588 | Design In-Memory File System | Solution | O(n) | O(h) | | Hard | Trie, Design |
| 587 | Erect the Fence | Solution | O(?) | O(?) | | Hard | Geometry |
| 583 | Delete Operation for Two Strings | Solution | O(m*n) | O(m*n) could be optimized to O(n) | | Medium | DP |
| 582 | Kill Process | Solution | O(n) | O(h) | | Medium | Stack |
| 581 | Shortest Unsorted Continuous Subarray | Solution | O(n) | O(1) | | Easy | Array, Sort |
| 576 | Out of Boundary Paths | Solution | O(Nmn) | O(m*n) | | Hard | DP, DFS |
| 575 | Distribute Candies | Solution | O(nlogn) | O(1) | | Easy | Array |
| 573 | Squirrel Simulation | Solution | O(n) | O(1) | | Medium | Math |
| 572 | Subtree of Another Tree | Solution | O(m*n) | O(1) | | Easy | Tree |
| 568 | Maximum Vacation Days | Solution | O(n^2*k) | O(n*k) | | Hard | DP |
| 567 | Permutation in String | Solution | O(l1 + 26*(l2 - l1)) | O(1) | | Medium | Sliding Windows, Two Pointers |
| 566 | Reshape the Matrix | Solution | O(m*n) | O(1) | | Easy | |
| 565 | Array Nesting | Solution | O(n) | O(n) | | Medium | |
| 563 | Binary Tree Tilt | Solution | O(n) | O(n) | | Easy | Tree Recursion |
| 562 | Longest Line of Consecutive One in Matrix | Solution | O(m*n) | O(m*n) | | Medium | Matrix DP |
| 561 | Array Partition I | Solution | O(nlogn) | O(1) | | Easy | Array |
| 560 | Subarray Sum Equals K | Solution | O(n) | O(n) | | Medium | Array, HashMap |
| 559 | Maximum Depth of N-ary Tree | Solution | O(n) | O(n) | | Easy | DFS, recursion |
| 557 | Reverse Words in a String III | Solution | O(n) | O(n) | | Easy | String |
| 556 | Next Greater Element III | Solution | O(n) | O(1) | | Medium | String |
| 555 | Split Concatenated Strings | Solution | O(n^2) | O(n) | | Medium | String |
| 554 | Brick Wall | Solution | O(n) (n is total number of bricks in the wall) | O(m) (m is width of the wall) | | Medium | HashMap |
| 553 | Optimal Division | Solution | O(n) | O(n) | | Medium | String, Math |
| 552 | Student Attendance Record II | Solution | O(n) | O(1) | | Hard | DP |
| 551 | Student Attendance Record I | Solution | O(n) | O(1) | | Easy | String |
| 549 | Binary Tree Longest Consecutive Sequence II | Solution | O(n) | O(n) | | Medium | Tree |
| 548 | Split Array with Equal Sum | Solution | O(n^2) | O(n) | | Medium | Array |
| 547 | Friend Circles | Solution | O(n^2) | O(n) | | Medium | Union Find |
| 546 | Remove Boxes | Solution | O(n^3) | O(n^3) | | Hard | DFS, DP |
| 545 | Boundary of Binary Tree | Solution | O(n) | O(n) | | Medium | Recursion |
| 544 | Output Contest Matches | Solution | O(n) | O(n) | | Medium | Recursion |
| 543 | Diameter of Binary Tree | Solution | O(n) | O(h) | | Easy | Tree/DFS/Recursion |
| 542 | 01 Matrix | Solution | O(m*n) | O(n) | | Medium | BFS |
| 541 | Reverse String II | Solution | O(n) | O(1) | | Easy | String |
| 540 | Single Element in a Sorted Array | Solution | O(n) | O(1) | | Medium | |
| 539 | Minimum Time Difference | Solution | O(logn) | O(1) | | Medium | String |
| 538 | Convert BST to Greater Tree | Solution | O(n) | O(h) | | Easy | Tree |
| 537 | Complex Number Multiplication | Solution | O(1) | O(1) | | Medium | Math, String |
| 536 | Construct Binary Tree from String | Solution | O(n) | O(h) | | Medium | Recursion, Stack |
| 535 | Encode and Decode TinyURL | Solution | O(1) | O(n) | | Medium | Design |
| 533 | Lonely Pixel II | Solution | O(m*n) | O(m) (m is number of rows) | | Medium | HashMap |
| 532 | K-diff Pairs in an Array | Solution | O(n) | O(n) | | Easy | HashMap |
| 531 | Lonely Pixel I | Solution | O(m*n) | O(1) | | Medium | |
| 530 | Minimum Absolute Difference in BST | Solution | O(n) | O(n) | | Easy | DFS |
| 529 | Minesweeper | Solution | O(m*n) | O(k) | | Medium | BFS |
| 527 | Word Abbreviation | Solution | O(n^2) | O(n) | | Hard | |
| 526 | Beautiful Arrangement | Solution | O(n) | O(h) | | Medium | Backtracking |
| 525 | Contiguous Array | Solution | O(n) | O(n) | | Medium | HashMap |
| 524 | Longest Word in Dictionary through Deleting | Solution | O(n) | O(n) | | Medium | Sort |
| 523 | Continuous Subarray Sum | Solution | O(n) | O(1) | | Medium | DP |
| 522 | Longest Uncommon Subsequence II | Solution | O(x*n^2) (x is average length of strings) | O(1) | | Medium | |
| 521 | Longest Uncommon Subsequence I | Solution | O(max(x,y)) (x and y are length of strings) | O(1) | | Easy | |
| 520 | Detect Capital | Solution | O(n) | O(1) | | Easy | |
| 517 | Super Washing Machines | Solution | | | | Hard | DP |
| 516 | Longest Palindromic Subsequence | Solution | O(n^2) | O(n^2) | | Medium | DP |
| 515 | Find Largest Value in Each Tree Row | Solution | O(n) | O(k) | | Medium | BFS |
| 514 | Freedom Trail | Solution | O(?) | O(?) | | Hard | DP |
| 513 | Find Bottom Left Tree Value | Solution | O(n) | O(k) | | Medium | BFS |
| 509 | Fibonacci Number | Solution | O(n) | O(n) | | Easy | Array |
| 508 | Most Frequent Subtree Sum | Solution | O(n) | O(n) | | Medium | DFS, Tree |
| 507 | Perfect Number | Solution | O(sqrt(n)) | O(1) | | Easy | Math |
| 506 | Relative Ranks | Solution | O(nlogn) | O(n) | | Easy | |
| 505 | The Maze II | Solution | O(m*n) | O(m*n) | | Medium | BFS |
| 504 | Base 7 | Solution | O(1) | O(1) | | Easy | |
| 503 | Next Greater Element II | Solution | O(n) | O(n) | | Medium | Stack |
| 502 | IPO | Solution | O(nlogn) | O(n) | | Hard | Heap, Greedy |
| 501 | Find Mode in Binary Tree | Solution | O(n) | O(k) | | Easy | Binary Tree |
| 500 | Keyboard Row | Solution | O(n) | O(1) | | Easy | |
| 499 | The Maze III | Solution | O(m*n) | O(m*n) | | Hard | BFS |
| 496 | Next Greater Element I | Solution | O(n*m) | O(1) | | Easy | |
| 498 | Diagonal Traverse | Solution | O(m*n) | O(1) | | Medium | |
| 495 | Teemo Attacking | Solution | O(n) | O(1) | | Medium | Array |
| 494 | Target Sum | Solution | O(2^n) | O(1) | | Medium | |
| 493 | Reverse Pairs | Solution | O(nlogn) | O(1) | | Hard | Recursion |
| 492 | Construct the Rectangle | Solution | O(n) | O(1) | | Easy | Array |
| 491 | Increasing Subsequences | Solution | O(n!) | O(n) | | Medium | Backtracking, DFS |
| 490 | The Maze | Solution | O(m*n) | O(m*n) | | Medium | BFS |
| 488 | Zuma Game | Solution | O(?) | O(?) | | Hard | DFS, Backtracking |
| 487 | Max Consecutive Ones II | Solution | O(n) | O(n) | | Medium | Array |
| 486 | Predict the Winner | Solution | O(2^n) | O(n^2) | | Medium | DP |
| 485 | Max Consecutive Ones | Solution | O(n) | O(1) | | Easy | Array |
| 484 | Find Permutation | Solution | O(n) | O(1) | | Medium | Array, String, Greedy |
| 483 | Smallest Good Base | Solution | O(logn) | O(1) | | Hard | Binary Search, Math |
| 482 | License Key Formatting | Solution | O(n) | O(n) | | Medium | |
| 481 | Magical String | Solution | O(?) | O(?) | | Medium | |
| 480 | Sliding Window Median | Solution | O(nlogk) | O(k) | | Hard | Heap |
| 479 | Largest Palindrome Product | Solution | O(n) | O(1) | | Easy | |
| 477 | Total Hamming Distance | Solution | O(n) | O(1) | | Medium | Bit Manipulation |
| 476 | Number Complement | Solution | O(n) | O(1) | | Easy | Bit Manipulation |
| 475 | Heaters | Solution | max(O(nlogn), O(mlogn)) - m is the length of houses, n is the length of heaters | O(1) | | Easy | Array Binary Search |
| 474 | Ones and Zeroes | Solution | O(n) | O(m*n) | | Medium | DP |
| 473 | Matchsticks to Square | Solution | O(n!) | O(n) | | Medium | Backtracking, DFS |
| 472 | Concatenated Words | Solution | O(n^2) | O(n) | | Hard | Trie, DP, DFS |
| 471 | Encode String with Shortest Length | Solution | O(n^3) | O(n^2) | | Hard | DP |
| 469 | Convex Polygon | Solution | O(n) | O(1) | | Medium | Math |
| 468 | Validate IP Address | Solution | O(n) | O(1) | | Medium | String |
| 467 | Unique Substrings in Wraparound String | Solution | O(n) | O(1) | | Medium | DP |
| 466 | Count The Repetitions | Solution | O(max(m,n)) | O(1) | | Hard | DP |
| 465 | Optimal Account Balancing | Solution | | | | Hard | DP |
| 464 | Can I Win | Solution | O(2^n) | O(n) | | Medium | DP |
| 463 | Island Perimeter | Solution | O(m*n) | O(1) | | Easy | |
| 462 | Minimum Moves to Equal Array Elements II | Solution | O(nlogn) | O(1) | | Medium | |
| 461 | Hamming Distance | Solution | O(n) | O(1) | | Easy | |
| 460 | LFU Cache | Solution | O(1) | O(n) | | Hard | Design, LinkedHashMap, HashMap |
| 459 | Repeated Substring Pattern | Solution | O(n) | O(n) | | Easy | String, KMP |
| 458 | Poor Pigs | Solution | O(1) | O(1) | | Easy | Math |
| 457 | Circular Array Loop | Solution | O(n) | O(1) | | Medium | |
| 456 | 132 Pattern | Solution | O(n) | O(n) | | Medium | Stack |
| 455 | Assign Cookies | Solution | O(n) | O(1) | | Easy | |
| 454 | 4Sum II | Solution | O(n) | O(n) | | Medium | HashMap |
| 453 | Minimum Moves to Equal Array Elements | Solution | O(n) | O(1) | | Easy | |
| 452 | Minimum Number of Arrows to Burst Balloons | Solution | O(nlogn) | O(1) | | Medium | Array, Greedy |
| 451 | Sort Characters By Frequency | Solution | O(nlogn) | O(n) | | Medium | HashMap |
| 450 | Delete Node in a BST | Solution | O(?) | O(?) | | Medium | Tree, Recursion |
| 449 | Serialize and Deserialize BST | Solution | O(n) | O(h) | | Medium | BFS |
| 448 | Find All Numbers Disappeared in an Array | Solution | O(n) | O(1) | | Easy | Array, HashMap |
| 447 | Number of Boomerangs | Solution | O(n^2) | O(n) | | Easy | HashMap |
| 446 | Arithmetic Slices II - Subsequence | Solution | O(n^2) | O(n^2) | | Hard | DP |
| 445 | Add Two Numbers II | Solution | O(max(m,n) | O(max(m,n)) | | Medium | Stack, LinkedList |
| 444 | Sequence Reconstruction | Solution | O(n) | O(n) | | Medium | Topological Sort, Graph |
| 443 | String Compression | Solution | O(n) | O(n) | | Easy | |
| 442 | Find All Duplicates in an Array | Solution | O(n) | O(1) | | Medium | Array |
| 441 | Arranging Coins | Solution | O(n) | O(1) | | Easy | |
| 440 | K-th Smallest in Lexicographical Order | Solution | O(n^2) | O(1) | | Hard | |
| 439 | Ternary Expression Parser | Solution | O(n) | O(n) | | Medium | Stack |
| 438 | Find All Anagrams in a String | Solution | O(n) | O(1) | | Easy | Sliding Window |
| 437 | Path Sum III | Solution | O(n^2) | O(n) | | Easy | DFS, recursion |
| 436 | Find Right Interval | Solution | O(nlogn) | O(n) | | Medium | Binary Search |
| 435 | Non-overlapping Intervals | Solution | O(nlogn) | O(1) | | Medium | Greedy |
| 434 | Number of Segments in a String | Solution | O(n) | O(1) | | Easy | |
| 432 | All O`one Data Structure | Solution | O(1) | O(n) | | Hard | Design |
| 429 | N-ary Tree Level Order Traversal | Solution | O(n) | O(n) | | Easy | BFS, Tree |
| 425 | Word Squares | Solution | O(n!) | O(n) | | Hard | Trie, Backtracking, Recursion |
| 424 | Longest Repeating Character Replacement | Solution | O(n) | O(1) | | Medium | Sliding Window |
| 423 | Reconstruct Original Digits from English | Solution | O(n) | O(1) | | Medium | Math |
| 422 | Valid Word Square | Solution | O(n) | O(1) | | Easy | |
| 421 | Maximum XOR of Two Numbers in an Array | Solution | O(n) | O(1) | | Medium | Bit Manipulation, Trie |
| 420 | Strong Password Checker | Solution | ? | ? | | Hard | |
| 419 | Battleships in a Board | Solution | O(m*n) | O(1) | | Medium | DFS |
| 418 | Sentence Screen Fitting | Solution | O(n) | O(1) | | Medium | |
| 417 | Pacific Atlantic Water Flow | Solution | O(mnMax(m,n)) | O(m*n) | | Medium | DFS |
| 416 | Partition Equal Subset Sum | Solution | O(m*n) | O(m*n) | | Medium | DP |
| 415 | Add Strings | Solution | O(n) | O(1) | | Easy | |
| 414 | Third Maximum Number | Solution | O(n) | O(1) | | Easy | |
| 413 | Arithmetic Slices | Solution | O(n) | O(1) | | Medium | DP |
| 412 | Fizz Buzz | Solution | O(n) | O(1) | | Easy | |
| 411 | Minimum Unique Word Abbreviation | Solution | O(?) | O(?) | | Hard | NP-Hard, Backtracking, Trie, Recursion |
| 410 | Split Array Largest Sum | Solution | O(nlogn) | O(1) | | Hard | Binary Search, DP |
| 409 | Longest Palindrome | Solution | O(n) | O(1) | | Easy | |
| 408 | Valid Word Abbreviation | Solution | O(n) | O(1) | | Easy | |
| 407 | Trapping Rain Water II | Solution | | | | Hard | Heap |
| 406 | Queue Reconstruction by Height | Solution | O(nlogn) | O(1) | | Medium | LinkedList, PriorityQueue |
| 405 | Convert a Number to Hexadecimal | Solution | O(n) | O(1) | | Easy | |
| 404 | Sum of Left Leaves | Solution | O(n) | O(h) | | Easy | |
| 403 | Frog Jump | Solution | O(n^2) | O(n^2) | | Hard | DP |
| 402 | Remove K Digits | Solution | O(n) | O(n) | | Medium | Greedy, Stack |
| 401 | Binary Watch | Solution | O(1) | O(1) | | Easy | |
| 400 | Nth Digit | Solution | O(n) | O(1) | | Easy | |
| 399 | Evaluate Division | Solution | O(n*n!) | O(n) | | Medium | Graph, DFS, Backtracking |
| 398 | Random Pick Index | Solution | | | | Medium | Reservoir Sampling |
| 397 | Integer Replacement | Solution | ? | ? | | Easy | BFS |
| 396 | Rotate Function | Solution | O(n^2) could be optimized to O(n) | O(1) | | Easy | |
| 395 | Longest Substring with At Least K Repeating Characters | Solution | O(n^2) | O(1) | | Medium | Recursion |
| 394 | Decode String | Solution | O(n) | O(n) | | Medium | Stack Depth-first-search |
| 393 | UTF-8 Validation | Solution | O(?) | O(?) | | Medium | Bit Manipulation |
| 392 | Is Subsequence | Solution | O(m*n) | O(1) | | Medium | Array, String |
| 391 | Perfect Rectangle | Solution | O(n) | O(1) | | Hard | |
| 390 | Elimination Game | Solution | O(logn) | O(1) | | Medium | |
| 389 | Find the Difference | Solution | O(n) | O(1) | | Easy | |
| 388 | Longest Absolute File Path | Solution | O(n) | O(d) | | Medium | Stack |
| 387 | First Unique Character in a String | Solution | O(n) | O(n) | | Easy | HashMap |
| 386 | Lexicographical Numbers | Solution | O(n) | O(1) | | Medium | |
| 385 | Mini Parser | Solution | O(n) | O(h) | | Medium | Stack |
| 384 | Shuffle an Array | Solution | O(n) | O(n) | | Medium | |
| 383 | Ransom Note | Solution | O(n) | O(n) | | Easy | String |
| 382 | Linked List Random Node | Solution | O(1) | O(n) | | Medium | Reservoir Sampling |
| 381 | Insert Delete GetRandom O(1) - Duplicates allowed | Solution | | | | Hard | |
| 380 | Insert Delete GetRandom O(1) | Solution | O(n) | O(1) | | Medium | Design, HashMap |
| 379 | Design Phone Directory | Solution | O(1) | O(n) | | Medium | |
| 378 | Kth Smallest Element in a Sorted Matrix | Solution | O(logm*n) | O(1) | | Medium | Binary Search |
| 377 | Combination Sum IV | Solution | O(n^2) | O(n) | | Medium | DP |
| 376 | Wiggle Subsequence | Solution | O(n) | O(1) | | Medium | DP, Greedy |
| 375 | Guess Number Higher or Lower II | Solution | O(n^2) | O(n^2) | | Medium | DP |
| 374 | Guess Number Higher or Lower | Solution | O(logn) | O(1) | | Easy | Binary Search |
| 373 | Find K Pairs with Smallest Sums | Solution | O(klogk) | O(k) | | Medium | Heap |
| 372 | Super Pow | Solution | O(n) | O(1) | | Medium | Math |
| 371 | Sum of Two Integers | Solution | O(n) | O(1) | | Easy | |
| 370 | Range Addition | Solution | O(n+k) | O(1) | | Medium | Array |
| 369 | Plus One Linked List | Solution | O(n) | O(1) | | Medium | Linked List |
| 368 | Largest Divisible Subset | Solution | O(n^2) | O(n) | | Medium | DP |
| 367 | Valid Perfect Square | Solution | O(n) | O(1) | | Medium | |
| 366 | Find Leaves of Binary Tree | Solution | O(n) | O(h) | | Medium | DFS |
| 365 | Water and Jug Problem | Solution | O(n) | O(1) | | Medium | Math |
| 364 | Nested List Weight Sum II | Solution | O(n) | O(h) | | Medium | DFS |
| 363 | Max Sum of Rectangle No Larger Than K | Solution | | | | Hard | DP |
| 362 | Design Hit Counter | Solution | O(1) amortized | O(k) | | Medium | Design |
| 361 | Bomb Enemy | Solution | O(?) | O(?) | | Medium | |
| 360 | Sort Transformed Array | Solution | O(n) | O(1) | | Medium | Two Pointers, Math |
| 359 | Logger Rate Limiter | Solution | amortized O(1) | O(k) | | Easy | HashMap |
| 358 | Rearrange String k Distance Apart | Solution | O(n) | O(n) | | Hard | HashMap, Heap, Greedy |
| 357 | Count Numbers with Unique Digits | Solution | O(n) | O(1) | | Medium | DP, Math |
| 356 | Line Reflection | Solution | O(n) | O(n) | | Medium | HashSet |
| 355 | Design Twitter | Solution | O(n) | O(n) | | Medium | Design, HashMap, Heap |
| 354 | Russian Doll Envelopes | Solution | O(nlogn) | O(1) | | Hard | DP, Binary Search |
| 353 | Design Snake Game | Solution | O(?) | O(?) | | Medium | |
| 352 | Data Stream as Disjoint Intervals | Solution | O(logn) | O(n) | | Hard | TreeMap |
| 351 | Android Unlock Patterns | Solution | O(?) | O(?) | | Medium | |
| 350 | Intersection of Two Arrays II | Solution | O(m+n) | O((m+n)) could be optimized | | Easy | HashMap, Binary Search |
| 349 | Intersection of Two Arrays | Solution | O(m+n) | O(min(m,n)) | | Easy | Two Pointers, Binary Search |
| 348 | Design Tic-Tac-Toe | Solution | O(1) | O(n) | | Medium | Design |
| 347 | Top K Frequent Elements | Solution | O(n) | O(k) k is is the number of unique elements in the given array | | Medium | HashTable, Heap, Bucket Sort |
| 346 | Moving Average from Data Stream | Solution | O(1) | O(w)) | | Easy | Queue |
| 345 | Reverse Vowels of a String | Solution | O(n) | O(1) | | Easy | String |
| 344 | Reverse String | Solution | O(n) | O(1) | | Easy | String |
| 343 | Integer Break | Solution | O(1) | O(1) | | Medium | Math |
| 342 | Power of Four | Solution | O(n) | O(1) | | Easy | Math |
| 341 | Flatten Nested List Iterator | Solution | O(n) | O(n) | | Medium | Stack |
| 340 | Longest Substring with At Most K Distinct Characters | Solution | O(n) | O(1) | | Hard | Sliding Window |
| 339 | Nested List Weight Sum | Solution | O(n) | O(h)) | | Easy | DFS |
| 338 | Counting Bits | Solution | O(nlogn) | O(h) | | Medium | |
| 337 | House Robber III | Solution | O(n) | O(n) | | Medium | DP |
| 336 | Palindrome Pairs | Solution | O(n^2) | O(n) | | Hard | |
| 335 | Self Crossing | Solution | O(n) | O(1) | | Hard | Math |
| 334 | Increasing Triplet Subsequence | Solution | O(n) | O(1) | | Medium | |
| 333 | Largest BST Subtree | Solution | O(n) | O(n) | | Medium | Tree |
| 332 | Reconstruct Itinerary | Solution | O(n) | O(n) | | Medium | Graph, DFS |
| 331 | Verify Preorder Serialization of a Binary Tree | Solution | O(n) | O(n) | | Medium | Stack |
| 330 | Patching Array | Solution | O(m+logn) | O(1) | | Hard | Greedy |
| 329 | Longest Increasing Path in a Matrix | Solution | O(m*n) | O(m*n) | | Hard | DFS, DP |
| 328 | Odd Even Linked List | Solution | O(n) | O(1) | | Medium | Linked List |
| 327 | Count of Range Sum | Solution | O(nlogn) | O(n) | | Hard | BST, Divide and Conquer |
| 326 | Power of Three | Solution | O(1) | O(1) | | Easy | Math |
| 325 | Maximum Size Subarray Sum Equals k | Solution | O(n) | O(n) | | Medium | HashTable |
| 324 | Wiggle Sort II | Solution | O(n) | O(n) | | Medium | Sort |
| 323 | Number of Connected Components in an Undirected Graph | Solution | O(?) | O(?) | | Medium | |
| 322 | Coin Change | Solution | O(n*k) | O(k) | | Medium | DP |
| 321 | Create Maximum Number | Solution | O(?) | O(?) | | Hard | |
| 320 | Generalized Abbreviation | Solution | O(n*2^n) | O(n) | | Medium | Backtracking, Bit Manipulation |
| 319 | Bulb Switcher | Solution | O(1) | O(1) | | Medium | Brainteaser |
| 318 | Maximum Product of Word Lengths | Solution | O(n^2) | O(n) | | Medium | |
| 317 | Shortest Distance from All Buildings | Solution | O(?) | O(?) | | Hard | |
| 316 | Remove Duplicate Letters | Solution | O(n) | O(1) | | Hard | Stack, Recursion, Greedy |
| 315 | Count of Smaller Numbers After Self | Solution | O(?) | O(?) | | Hard | Tree |
| 314 | Binary Tree Vertical Order Traversal | Solution | O(n) | O(n) | | Medium | HashMap, BFS |
| 313 | Super Ugly Number | Solution | O(?) | O(?) | | Medium | |
| 312 | Burst Balloons | Solution | O(?) | O(?) | | Hard | DP |
| 311 | Sparse Matrix Multiplication | Solution | O(mnl) | O(m*l) | | Medium | |
| 310 | Minimum Height Trees | Solution | ? | ? | | Medium | |
| 309 | Best Time to Buy and Sell Stock with Cooldown | Solution | O(n) | O(1) | | Medium | DP |
| 308 | Range Sum Query 2D - Mutable | Solution | ? | ? | | Hard | Tree |
| 307 | Range Sum Query - Mutable | Solution | ? | ? | | Medium | Tree |
| 306 | Additive Number | Solution | O(n^2) | O(n) | | Medium | |
| 305 | Number of Islands II | Solution | ? | ? | | Hard | Union Find |
| 304 | Range Sum Query 2D - Immutable | Solution | ? | ? | | Medium | |
| 303 | Range Sum Query - Immutable | Solution | O(n) | O(1) | | Easy | |
| 302 | Smallest Rectangle Enclosing Black Pixels | Solution | ? | O(m*n) | | Hard | DFS, BFS |
| 301 | Remove Invalid Parentheses | Solution | ? | ? | | Hard | BFS |
| 300 | Longest Increasing Subsequence | Solution | O(logn) | O(n) | | Medium | DP |
| 299 | Bulls and Cows | Solution | O(n) | O(1) | | Easy | |
| 298 | Binary Tree Longest Consecutive Sequence | Solution | O(n) | O(n) | | Medium | Tree |
| 297 | Serialize and Deserialize Binary Tree | Solution | O(n) | O(h) | | Hard | BFS |
| 296 | Best Meeting Point | Solution | ? | ? | | Hard | |
| 295 | Find Median from Data Stream | Solution | O(logn) | O(n) | | Hard | Heap |
| 294 | Flip Game II | Solution | O(?) | O(?) | | Medium | Backtracking |
| 293 | Flip Game | Solution | O(n) | O(1) | | Easy | |
| 292 | Nim Game | Solution | O(1) | O(1) | | Easy | |
| 291 | Word Pattern II | Solution | O(n) | O(n) | | Hard | Recursion, Backtracking |
| 290 | Word Pattern | Solution | O(n) | O(n) | | Easy | HashMap |
| 289 | Game of Life | Solution | O(m*n) | O(m*n), could be optimized to O(1) | | Medium | |
| 288 | Unique Word Abbreviation | Solution | O(n) | O(1) | | Easy | |
| 287 | Find the Duplicate Number | Solution | O(n) | O(1) | | Medium | |
| 286 | Walls and Gates | Solution | O(m*n) | O(g) | | Medium | BFS |
| 285 | Inorder Successor In BST | Solution | O(h) | O(1) | | Medium | Tree |
| 284 | Peeking Iterator | Solution | O(n) | O(n) | | Medium | Design |
| 283 | Move Zeroes | Solution | O(n) | O(1) | | Easy | |
| 282 | Expression Add Operators | Solution | O(?) | O(?) | | Hard | |
| 281 | Zigzag Iterator | Solution | O(1) | O(k) | | Medium | |
| 280 | Wiggle Sort | Solution | O(n) | O(1) | | Medium | |
| 279 | Perfect Squares | Solution | O(n) | O(1) | | Medium | |
| 278 | First Bad Version | Solution | O(logn) | O(1) | | Easy | Binary Search |
| 277 | Find the Celebrity | Solution | O(n) | O(1) | | Medium | |
| 276 | Paint Fence | Solution | O(n) | O(1) | | Easy | DP |
| 275 | H-Index II | Solution | O(logn) | O(1) | | Medium | Binary Search |
| 274 | H-Index | Solution | O(nlogn) | O(1) | | Medium | |
| 273 | Integer to English Words | Solution | O(n) | O(1) | | Hard | Math, String |
| 272 | Closest Binary Search Tree Value II | Solution | O(h+k) | O(h) | | Hard | Stack |
| 271 | Encode and Decode Strings | Solution | O(n) | O(1) | | Medium | |
| 270 | Closest Binary Search Tree Value | Solution | O(h) | O(1) | | Easy | DFS |
| 269 | Alien Dictionary | Solution | O(?) | O(?) | | Hard | Topological Sort |
| 268 | Missing Number | Solution | O(n) | O(1) | | Easy | Bit Manipulation |
| 267 | Palindrome Permutation II | Solution | O(n*n!) | O(n) | | Medium | |
| 266 | Palindrome Permutation | Solution | O(n) | O(1) | | Easy | |
| 265 | Paint House II | Solution | O(n*k) | O(1) | | Hard | DP |
| 264 | Ugly Number II | Solution | O(n) | O(n) | | Medium | DP |
| 263 | Ugly Number | Solution | O(n) | O(1) | | Easy | |
| 261 | Graph Valid Tree | Solution | O(V+E) | O(V+E) | | Medium | |
| 260 | Single Number III | Solution | O(n) | O(n) | | Medium | |
| 259 | 3Sum Smaller | Solution | O(n^2) | O(1) | | Medium | |
| 258 | Add Digits | Solution | O(1) | O(1) | | Easy | |
| 257 | Binary Tree Paths | Solution | O(n*h) | O(h) | | | DFS/Recursion |
| 256 | Paint House | Solution | O(n) | O(1) | | Medium | DP |
| 255 | Verify Preorder Sequence in Binary Search Tree | Solution | O(n) | O(h) | | Medium | Tree |
| 254 | Factor Combinations | Solution | O(nlogn) | O(nlogn) | | Medium | Backtracking |
| 253 | Meeting Rooms II | Solution | O(nlogn) | O(h) | | Medium | Heap |
| 252 | Meeting Rooms | Solution | O(nlogn) | O(1) | | Easy | |
| 251 | Flatten 2D Vector | Solution | O(1) | O(m*n) | | Medium | |
| 250 | Count Univalue Subtrees | Solution | O(n) | O(h) | | Medium | DFS |
| 249 | Group Shifted Strings | Solution | O(nlogn) | O(n) | | | |
| 248 | Strobogrammatic Number III | Solution | O(?) | O(?) | | Hard | Recursion, DFS |
| 247 | Strobogrammatic Number II | Solution | O(n^2) | O(n) | | Medium | Recursion |
| 246 | Strobogrammatic Number | Solution | O(n) | O(1) | | Easy | |
| 245 | Shortest Word Distance III | Solution | O(n) | O(1) | | Medium | |
| 244 | Shortest Word Distance II | Solution | O(n) | O(n) | | Medium | HashMap |
| 243 | Shortest Word Distance | Solution | O(n) | O(1) | | Easy | |
| 242 | Valid Anagram | Solution | O(n) | O(1) | | Easy | |
| 241 | Different Ways to Add Parentheses | Solution | O(O(n * 4^n / n^(3/2))) | O(n * 4^n / n^(3/2)) | | Medium | Divide and Conquer |
| 240 | Search a 2D Matrix II | Solution | O(m+n) | O(1) | | Medium | Binary Search |
| 239 | Sliding Window Maximum | Solution | O(nlogn) | O(k) | | Hard | Heap |
| 238 | Product of Array Except Self | Solution | O(n) | O(1) | | Medium | Array |
| 237 | Delete Node in a Linked List | Solution | O(1) | O(1) | | Easy | LinkedList |
| 236 | Lowest Common Ancestor of a Binary Tree | Solution | O(n) | O(h) | | Medium | DFS |
| 235 | Lowest Common Ancestor of a Binary Search Tree | Solution | O(h) | O(1) | | Easy | DFS |
| 234 | Palindrome Linked List | Solution | O(n) | O(1) | | Easy | Linked List |
| 233 | Number of Digit One | Solution | O(n) | O(1) | | Hard | Math |
| 232 | Implement Queue using Stacks | Solution | O(n) | O(n) | | Medium | Stack, Design |
| 231 | Power of Two | Solution | O(1) | O(1) | | Easy | |
| 230 | Kth Smallest Element in a BST | Solution | O(n) | O(k) | | Medium | Tree |
| 229 | Majority Element II | Solution | O(n) | O(1) | | Medium | |
| 228 | Summary Ranges | Solution | O(n) | O(1) | | Medium | Array |
| 227 | Basic Calculator II | Solution | O(n) | O(n) | | Medium | String |
| 226 | Invert Binary Tree | Solution | O(n) | O(h) | | Easy | DFS, recursion |
| 225 | Implement Stack using Queues | Solution | O(n) | O(n) | | Easy | Stack, Queue |
| 224 | Basic Calculator | Solution | ? | ? | | Hard | |
| 223 | Rectangle Area | Solution | O(1) | O(1) | | Easy | |
| 222 | Count Complete Tree Nodes | Solution | O(?) | O(h) | | Medium | Recursion |
| 221 | Maximal Square | Solution | O(?) | O(h) | | Medium | Recursion |
| 220 | Contains Duplicate III | Solution | O(nlogn) | O(n) | | Medium | TreeSet |
| 219 | Contains Duplicate II | Solution | O(n) | O(n) | | Easy | HashMap |
| 218 | The Skyline Problem | Solution | O(n) | O(n) | | Hard | TreeMap, Design |
| 217 | Contains Duplicate | Solution | O(n) | O(n) | | Easy | HashSet |
| 216 | Combination Sum III | Solution | O(k * C(n, k)) | O(k) | | Medium | Backtracking |
| 215 | Kth Largest Element in an Array | Solution | O(nlogn) | O(n) | | Medium | Heap |
| 214 | Shortest Palindrome | Solution | O(?) | O(?) | | Hard | KMP |
| 213 | House Robber II | Solution | O(n) | O(n) | | Medium | DP |
| 212 | Word Search II | Solution | O(mnl) | O(l) | | Hard | Trie |
| 211 | Add and Search Word - Data structure design | Solution | O(n) | O(h) | | Medium | Trie |
| 210 | Course Schedule II | Solution | O(?) | O(?) | | Medium | |
| 209 | Minimum Size Subarray Sum | Solution | O(n) | O(1) | | Medium | |
| 208 | Implement Trie | Solution | O(n) | O(1) | | Medium | Trie |
| 207 | Course Schedule | Solution | O(?) | O(?) | | Medium | |
| 206 | Reverse Linked List | Solution | O(n) | O(1) | | Easy | Linked List |
| 205 | Isomorphic Strings | Solution | O(n) | O(1) | | Easy | |
| 204 | Count Primes | Solution | O(nloglogn) | O(n) | | Easy | The Sieve of Eratosthenes |
| 203 | Remove Linked List Elements | Solution | O(n) | O(1) | | Easy | |
| 202 | Happy Number | Solution | O(k) | O(k) | | Easy | |
| 201 | Bitwise AND of Numbers Range | Solution | O(min(m,n)) | O(1) | | Medium | Bit Manipulation |
| 200 | Number of Islands | Solution | O(m*n) | O(m*n) | | Medium | Union Find, DFS |
| 199 | Binary Tree Right Side View | Solution | O(n) | O(h) | | Medium | BFS |
| 198 | House Robber | Solution | O(n) | O(n) | | Easy | DP |
| 191 | Number of 1 Bits | Solution | O(1) | O(1) | | Easy | Bit Manipulation |
| 190 | Reverse Bits | Solution | O(n) | O(1) | | Easy | Bit Manipulation |
| 189 | Rotate Array | Solution | O(n) | O(n), could be optimized to O(1) | | Easy | |
| 188 | Best Time to Buy and Sell Stock IV | Solution | O(n*k) | O(n*k) | | Hard | DP |
| 187 | Repeated DNA Sequences | Solution | O(n) | O(n) | | Medium | |
| 186 | Reverse Words in a String II | Solution | O(n) | O(1) | | Medium | |
| 179 | Largest Number | Solution | O(?) | O(?) | | Medium | |
| 174 | Dungeon Game | Solution | O(m*n) | O(m*n) | | Hard | DP |
| 173 | Binary Search Tree Iterator | Solution | O(1) | O(h) | | Medium | Stack, Design |
| 172 | Factorial Trailing Zeroes | Solution | O(logn) | O(1) | | Easy | |
| 171 | Excel Sheet Column Number | Solution | O(n) | O(1) | | Easy | |
| 170 | Two Sum III - Data structure design | Solution | O(n) | O(n) | | Easy | |
| 169 | Majority Element | Solution | O(n) | O(1) | | Easy | |
| 168 | Excel Sheet Column Title | Solution | O(n) | O(1) | | Easy | |
| 167 | Two Sum II - Input array is sorted | Solution | O(n) | O(1) | | Easy | Binary Search |
| 166 | Fraction to Recurring Decimal | Solution | O(1) | O(1) | | Medium | HashMap |
| 165 | Compare Version Numbers | Solution | O(n) | O(1) | | Easy | |
| 164 | Maximum Gap | Solution | O(n) | O(n) | | Hard | |
| 163 | Missing Ranges | Solution | O(n) | O(1) | | | |
| 162 | Find Peak Element | Solution | O(1) | O(logn)/O(n) | | Binary Search | |
| 161 | One Edit Distance | Solution | O(n) | O(1) | | | |
| 160 | Intersection of Two Linked Lists | Solution | O(m+n) | O(1) | | Easy | Linked List |
| 159 | Longest Substring with At Most Two Distinct Characters | Solution | O(n) | O(1) | | Hard | String, Sliding Window |
| 158 | Read N Characters Given Read4 II - Call multiple times | Solution | O(n) | O(1) | | Hard | |
| 157 | Read N Characters Given Read4 | Solution | O(n) | O(1) | | Easy | |
| 156 | Binary Tree Upside Down | Solution | O(n) | O(h) | | Medium | Tree, Recursion |
| 155 | Min Stack | Solution | O(1) | O(n) | | Easy | Stack |
| 154 | Find Minimum in Rotated Sorted Array II | Solution | O(logn) | O(1) | | Hard | Array, Binary Search |
| 153 | Find Minimum in Rotated Sorted Array | Solution | O(logn) | O(1) | | Medium | Array, Binary Search |
| 152 | Maximum Product Subarray | Solution | O(n) | O(1) | | Medium | Array |
| 151 | Reverse Words in a String | Solution | O(n) | O(n) | | Medium | String |
| 150 | Evaluate Reverse Polish Notation | Solution | O(?) | O(?) | | Medium | |
| 149 | Max Points on a Line | Solution | O(?) | O(?) | | Hard | |
| 148 | Sort List | Solution | O(nlogn) | O(h) | | Medium | Linked List, Sort |
| 147 | Insertion Sort List | Solution | O(n^2) | O(1) | | Medium | Linked List |
| 146 | LRU Cache | Solution | amortized O(1) | O(k) | | Hard | Doubly Linked List, LinkedHashMap |
| 145 | Binary Tree Postorder Traversal | Solution | O(n) | O(h) | | Hard | Binary Tree |
| 144 | Binary Tree Preorder Traversal | Solution | O(n) | O(h) | | Medium | Binary Tree |
| 143 | Reorder List | Solution | O(n) | O(1) | | Medium | |
| 142 | Linked List Cycle II | Solution | O(n) | O(1) | | Medium | Linked List |
| 141 | Linked List Cycle | Solution | O(n) | O(1) | | Easy | Linked List |
| 140 | Word Break II | Solution | ? | O(n^2) | | Hard | Backtracking/DFS |
| 139 | Word Break | Solution | O(n^2) | O(n) | | Medium | DP, Pruning |
| 138 | Copy List with Random Pointer | Solution | O(n) | O(n) | | Medium | LinkedList, HashMap |
| 137 | Single Number II | Solution | O(n) | O(1) | | Medium | Bit Manipulation |
| 136 | Single Number | Solution | O(n) | O(1) | | Easy | Bit Manipulation |
| 135 | Candy | Solution | O(n) | O(1) | | Hard | Greedy |
| 134 | Gas Station | Solution | O(n) | O(1) | | Medium | Greedy |
| 133 | Clone Graph | Solution | O(n) | O(n) | | Medium | HashMap, BFS, Graph |
| 132 | Palindrome Partitioning II | Solution | O(n^2) | O(n^2) | | Hard | |
| 131 | Palindrome Partitioning | Solution | O(n^2) | O(n^2) | | Medium | |
| 130 | Surrounded Regions | Solution | O(?) | O(?) | | Medium | |
| 129 | Sum Root to Leaf Numbers | Solution | O(n) | O(h) | | Medium | DFS |
| 128 | Longest Consecutive Sequence | Solution | O(n) | O(n) | | Hard | Union Find |
| 127 | Word Ladder | Solution | O(n^2) | O(n) | | Medium | BFS |
| 126 | Word Ladder II | Solution | O(?) | O(?) | | Hard | BFS |
| 125 | Valid Palindrome | Solution | O(n) | O(1) | | Easy | Two Pointers |
| 124 | Binary Tree Maximum Path Sum | Solution | O(n) | O(h) | | Hard | Tree, DFS |
| 123 | Best Time to Buy and Sell Stock III | Solution | O(n) | O(1) | | Hard | DP |
| 122 | Best Time to Buy and Sell Stock II | Solution | O(n) | O(1) | | Easy | Greedy |
| 121 | Best Time to Buy and Sell Stock | Solution | O(n) | O(1) | | Easy | |
| 120 | Triangle | Solution | O(m*n) | O(n) | | Medium | DP |
| 119 | Pascal's Triangle II | Solution | O(n^2) | O(k) | | Easy | |
| 118 | Pascal's Triangle | Solution | O(n^2) | O(1) | | Easy | |
| 117 | Populating Next Right Pointers in Each Node II | Solution | O(n) | O(1) | | Medium | BFS |
| 116 | Populating Next Right Pointers in Each Node | Solution | O(n) | O(1) | | Medium | BFS |
| 115 | Distinct Subsequences | Solution | O(m*n) | O(m*n) | | Hard | DP |
| 114 | Flatten Binary Tree to Linked List | Solution | O(n) | O(h) | | Medium | Tree |
| 113 | Path Sum II | Solution | O(n) | O(h) | | Medium | DFS, Backtracking |
| 112 | Path Sum | Solution | O(n) | O(1) | | Easy | DFS |
| 111 | Minimum Depth of Binary Tree | Solution | O(n) | O(1)~O(h) | | Easy | BFS, DFS |
| 110 | Balanced Binary Tree | Solution | O(n) | O(1)~O(h) | | Easy | DFS |
| 109 | Convert Sorted List to Binary Search Tree | Solution | O(n) | O(h) | | Medium | DFS, Recursion |
| 108 | Convert Sorted Array to Binary Search Tree | Solution | O(n) | O(h) | | Easy | Tree |
| 107 | Binary Tree Level Order Traversal II | Solution | O(nlogn) | O(h) | | Easy | BFS |
| 106 | Construct Binary Tree from Inorder and Postorder Traversal | Solution | O(n) | O(n) | | Medium | Recursion, Tree |
| 105 | Construct Binary Tree from Preorder and Inorder Traversal | Solution | O(n) | O(n) | | Medium | Recursion, Tree |
| 104 | Maximum Depth of Binary Tree | Solution | O(n) | O(h) | | Easy | DFS |
| 103 | Binary Tree Zigzag Level Order Traversal | Solution | O(n) | O(h) | | Medium | BFS,DFS |
| 102 | Binary Tree Level Order Traversal | Solution | O(n) | O(h) | | Medium | BFS |
| 101 | Symmetric Tree | Solution | O(n) | O(h) | | Easy | DFS |
| 100 | Same Tree | Solution | O(n) | O(h) | | Easy | DFS |
| 99 | Recover Binary Search Tree | Solution | O(?) | O(?) | | Hard | |
| 98 | Validate Binary Search Tree | Solution | O(n) | O(h) | | Medium | DFS/Recursion |
| 97 | Interleaving String | Solution | O(?) | O(?) | | Hard | DP |
| 96 | Unique Binary Search Trees | Solution | O(n^2) | O(n) | | Medium | Recursion, DP |
| 95 | Unique Binary Search Trees II | Solution | O(?) | O(?) | | Medium | Recursion |
| 94 | Binary Tree Inorder Traversal | Solution | O(n) | O(h) | | Medium | Binary Tree |
| 93 | Restore IP Addresses | Solution | O(?) | O(?) | | Medium | Backtracking |
| 92 | Reverse Linked List II | Solution | O(n) | O(1) | | Medium | |
| 91 | Decode Ways | Solution | O(n) | O(n) | | Medium | DP |
| 90 | Subsets II | Solution | O(n^2) | O(1) | | Medium | Backtracking |
| 89 | Gray Code | Solution | O(n) | O(1) | | Medium | Bit Manipulation |
| 88 | Merge Sorted Array | Solution | O(max(m,n)) | O(1) | | Easy | |
| 87 | Scramble String | Solution | O(n^4) | O(n^3 | | Hard | Recursion |
| 86 | Partition List | Solution | O(n) | O(1) | | Medium | Linked List |
| 85 | Maximal Rectangle | Solution | O(m*n) | O(n) | | Hard | DP |
| 84 | Largest Rectangle in Histogram | Solution | O(n) | O(n) | | Hard | Array, Stack |
| 83 | Remove Duplicates from Sorted List | Solution | O(n) | O(1) | | Easy | Linked List |
| 82 | Remove Duplicates from Sorted List II | Solution | O(n) | O(1) | | Medium | Linked List |
| 81 | Search in Rotated Sorted Array II | Solution | O(logn) | O(1) | | Medium | Binary Search |
| 80 | Remove Duplicates from Sorted Array II | Solution | O(n) | O(n) | | Medium | |
| 79 | Word Search | Solution | O((m*n)^2) | O(m*n) | | Medium | Backtracking, DFS |
| 78 | Subsets | Solution | O(n^2) | O(1) | | Medium | Backtracking |
| 77 | Combinations | Solution | O(n!) | O(n) | | Medium | Backtracking |
| 76 | Minimum Window Substring | Solution | O(n) | O(k) | | Hard | Two Pointers |
| 75 | Sort Colors | Solution | O(n) | O(1) | | Medium | Two Pointers |
| 74 | Search a 2D Matrix | Solution | O(log(m*n)) | O(1) | | Medium | Binary Search |
| 73 | Set Matrix Zeroes | Solution | O(mn) | O(1) | | Medium | |
| 72 | Edit Distance | Solution | O(m*n) | O(m+n) | | Hard | |
| 71 | Simplify Path | Solution | O(n) | O(n) | | Medium | Stack |
| 70 | Climbing Stairs | Solution | O(n) | O(n) | | Easy | DP |
| 69 | Sqrt(x) | Solution | O(logn) | O(1) | | Easy | |
| 68 | Text Justification | Solution | O(n) | O(1) | | Hard | |
| 67 | Add Binary | Solution | O(n) | O(1) | | Easy | |
| 66 | Plus One | Solution | O(n) | O(1) | | Easy | |
| 65 | Valid Number | Solution | O(n) | O(1) | | Hard | |
| 64 | Minimum Path Sum | Solution | O(m*n) | O(m*n) | | Medium | DP |
| 63 | Unique Paths II | Solution | O(m*n) | O(m*n) | | Medium | DP |
| 62 | Unique Paths | Solution | O(m*n) | O(m*n) | | Medium | DP |
| 61 | Rotate List | Solution | O(n) | O(1) | | Medium | Linked List |
| 60 | Permutation Sequence | Solution | O(n^2) | O(n) | | Medium | Math, Backtracking |
| 59 | Spiral Matrix II | Solution | O(n) | O(n) | | Medium | |
| 58 | Length of Last Word | Solution | O(n) | O(1) | | Easy | |
| 57 | Insert Intervals | Solution | O(n) | O(1) | | Hard | Array, Sort |
| 56 | Merge Intervals | Solution | O(n*logn) | O(1) | | Medium | Array, Sort |
| 55 | Jump Game | Solution | O(n) | O(1) | | Medium | Greedy |
| 54 | Spiral Matrix | Solution | O(m*n) | O(m*n) | | Medium | Array |
| 53 | Maximum Subarray | Solution | O(n) | O(1) | | Easy | Array |
| 52 | N-Queens II | Solution | O(n!) | O(n) | | Hard | Backtracking |
| 51 | N-Queens | Solution | O(n!) | O(n) | | Hard | |
| 50 | Pow(x, n) | Solution | O(logn) | O(logn) | | Medium | |
| 49 | Group Anagrams | Solution | O(m*klogk) | O(m*k) | | Medium | HashMap |
| 48 | Rotate Image | Solution | O(n^2) | O(1) | | Medium | Array |
| 47 | Permutations II | Solution | O(n*n!) | O(n) | | Medium | Backtracking |
| 46 | Permutations | Solution | O(n*n!) | O(n) | | Medium | Backtracking |
| 45 | Jump Game II | Solution | O(n) | O(1) | | Hard | Array, Greedy |
| 44 | Wildcard Matching | Solution | O(m*n) | O(m*n) | | Hard | Backtracking, DP, Greedy, String |
| 43 | Multiply Strings | Solution | O(n) | O(1) | | Medium | Array, String |
| 42 | Trapping Rain Water | Solution | O(n) | O(1) | | Hard | |
| 41 | First Missing Positive | Solution | O(n) | O(1) | | Hard | Array |
| 40 | Combination Sum II | Solution | O(k*n^k) | O(k) | | Medium | Backtracking |
| 39 | Combination Sum | Solution | O(k*n^k) | O(k) | | Medium | Backtracking |
| 38 | Count and Say | Solution | O(n*2^n) | O(2^n) | | Easy | Recursion, LinkedList |
| 37 | Sudoku Solver | Solution | O((9!)^9) | O(1) | | Hard | |
| 36 | Valid Sudoku | Solution | O(1) | O(1) | | Medium | |
| 35 | Search Insert Position | Solution | O(n) | O(1) | | Easy | Array |
| 34 | Search for a Range | Solution | O(logn) | O(1) | | Medium | Array, Binary Search |
| 33 | Search in Rotated Sorted Array | Solution | O(logn) | O(1) | | Medium | Binary Search |
| 32 | Longest Valid Parentheses | Solution | O(n) | O(n) | | Hard | Stack, DP |
| 31 | Next Permutation | Solution | O(n) | O(1) | | Medium | Array |
| 30 | Substring with Concatenation of All Words | Solution | O(n^2) | O(n) | | Hard | HashMap |
| 29 | Divide Two Integers | Solution | O(?) | O(?) | | Medium | |
| 28 | Implement strStr() | Solution | O(n) | O(1) | | Easy | String |
| 27 | Remove Element | Solution | O(n) | O(1) | | Easy | |
| 26 | Remove Duplicates from Sorted Array | Solution | O(n) | O(1) | | Easy | Array |
| 25 | Reverse Nodes in k-Group | Solution | O(n) | O(1) | | Hard | Recursion, LinkedList |
| 24 | Swap Nodes in Pairs | Solution | O(n) | O(h) | | Medium | Recursion, LinkedList |
| 23 | Merge k Sorted Lists | Solution | O(n*logk) | O(k) | | Hard | Heap |
| 22 | Generate Parentheses | Solution | TBD | O(n) | | Medium | Backtracking |
| 21 | Merge Two Sorted Lists | Solution | O(n) | O(h) | | Easy | Recursion |
| 20 | Valid Parentheses | Solution | O(n) | O(n) | | Easy | Stack |
| 19 | Remove Nth Node From End of List | Solution | O(n) | O(1) | | Medium | Linked List |
| 18 | 4 Sum | Solution | O(n^2) | O(1) | | Medium | Two Pointers |
| 17 | Letter Combinations of a Phone Number | Solution | O(n*4^n) | O(n) | | Medium | Backtracking |
| 16 | 3Sum Closest | Solution | O(nlogn) | O(1) | | Medium | Two Pointers |
| 15 | 3Sum | Solution | O(n^2) | O(1) | | Medium | Two Pointers, Binary Search |
| 14 | Longest Common Prefix | Solution | O(S) (S is the sum of all characters in all strings) | O(1) | | Easy | |
| 13 | Roman to Integer | Solution | O(1) | O(1) | | Easy | Math, String |
| 12 | Integer to Roman | Solution | O(1) | O(1) | | Medium | Math, String |
| 11 | Container With Most Water | Solution | O(n) | O(1) | | Medium | |
| 10 | Regular Expression Matching | Solution | O(m*n) | O(m*n) | | Hard | DP |
| 9 | Palindrome Number | Java,C++ | O(n) | O(1) | | Easy | |
| 8 | String to Integer (atoi) | Solution | O(n) | O(1) | | Medium | |
| 7 | Reverse Integer | Solution | O(1) | O(1) | | Easy | |
| 6 | ZigZag Conversion | Solution | O(n) | O(n) | | Easy | |
| 5 | Longest Palindromic Substring | Solution | O(n^2) | O(1) | | Medium | |
| 4 | Median of Two Sorted Arrays | Solution | ? | ? | | Hard | Divide and Conquer |
| 3 | Longest Substring Without Repeating Characters | Solution | O(n) | O(k) | | Medium | HashMap, Sliding Window |
| 2 | Add Two Numbers | Solution | O(max(m,n)) | O(1) | | Medium | LinkedList |
| 1 | Two Sum | Java,C++ | O(n) | O(n) | 📺 | Easy | HashMap |
