| 526 | Beautiful Arrangement | | Medium |
| 525 | Contiguous Array | | Medium |
| 524 | | | |
| 523 | | | |
| 522 | | | |
| 521 | | | |
| 520 | Detect Capital | Ruby | Easy |
| 519 | | | |
| 518 | | | |
| 517 | Super Washing Machines | | Hard |
| 516 | Longest Palindromic Subsequence | | Medium |
| 515 | Find Largest Value in Each Tree Row | | Medium |
| 514 | | | |
| 513 | Find Bottom Left Tree Value | | Medium |
| 512 | | | |
| 511 | | | |
| 510 | | | |
| 509 | | | |
| 508 | Most Frequent Subtree Sum | | Medium |
| 507 | | | |
| 506 | Relative Ranks | Ruby | Easy |
| 505 | The Maze II | 🔒 | Medium |
| 504 | Base 7 | Ruby | Easy |
| 503 | Next Greater Element II | | Medium |
| 502 | IPO | | Hard |
| 501 | Find Mode in Binary Search Tree | Ruby | Easy |
| 500 | Keyboard Row | Ruby | Easy |
| 499 | The Maze III | | Hard |
| 498 | Diagonal Traverse | | Medium |
| 497 | | | |
| 496 | Next Greater Element I | | Easy |
| 495 | Teemo Attacking | | Medium |
| 494 | Target Sum | | Medium |
| 493 | Reverse Pairs | | Hard |
| 492 | Construct the Rectangle | | Easy |
| 491 | Increasing Subsequences | | Medium |
| 490 | The Maze | 🔒 | Medium |
| 489 | | | |
| 488 | Zuma Game | | Hard |
| 487 | Max Consecutive Ones II | 🔒 | Medium |
| 486 | Predict the Winner | | Medium |
| 485 | Max Consecutive Ones | | Easy |
| 484 | Find Permutation | 🔒 | Medium |
| 483 | Smallest Good Base | | Hard |
| 482 | License Key Formatting | | Medium |
| 481 | Magical String | | Medium |
| 480 | Sliding Window Median | | Hard |
| 479 | | | |
| 478 | | | |
| 477 | Total Hamming Distance | | Medium |
| 476 | Number Complement | | Easy |
| 475 | Heaters | | Easy |
| 474 | Ones and Zeroes | | Medium |
| 473 | Matchsticks to Square | | Medium |
| 472 | Concatenated Words | | Hard |
| 471 | Encode String with Shortest Length | 🔒 | Hard |
| 470 | | | |
| 469 | Convex Polygon | 🔒 | Medium |
| 468 | Validate IP Address | Ruby | Medium |
| 467 | Unique Substrings in Wraparound String | | Medium |
| 466 | Count The Repetitions | | Hard |
| 465 | Optimal Account Balancing | 🔒 | Hard |
| 464 | Can I Win | | Medium |
| 463 | Island Perimeter | | Easy |
| 462 | Minimum Moves to Equal Array Elements II | | Medium |
| 461 | Hamming Distance | | Easy |
| 460 | LFU Cache | | Hard |
| 459 | Repeated Substring Pattern | | Easy |
| 458 | | | |
| 457 | | | |
| 456 | 132 Pattern | | Medium |
| 455 | Assign Cookies | Ruby | Easy |
| 454 | 4Sum II | | Medium |
| 453 | Minimum Moves to Equal Array Elements | Ruby | Easy |
| 452 | Minimum Number of Arrows to Burst Balloons | | Medium |
| 451 | Sort Characters By Frequency | Ruby | Medium |
| 450 | Delete Node in a BST | | Medium |
| 449 | Serialize and Deserialize BST | Ruby | Medium |
| 448 | Find All Numbers Disappeared in an Array | Ruby | Easy |
| 447 | Number of Boomerangs | | Easy |
| 446 | Arithmetic Slices II - Subsequence | | Hard |
| 445 | Add Two Numbers II | | Medium |
| 444 | Sequence Reconstruction | 🔒 | Medium |
| 443 | | | |
| 442 | Find All Duplicates in an Array | | Medium |
| 441 | Arranging Coins | | Easy |
| 440 | K-th Smallest in Lexicographical Order | | Hard |
| 439 | Ternary Expression Parser | 🔒 | Medium |
| 438 | Find All Anagrams in a String | | Easy |
| 437 | Path Sum III | | Easy |
| 436 | Find Right Interval | | Medium |
| 435 | Non-overlapping Intervals | | Medium |
| 434 | Number of Segments in a String | | Easy |
| 433 | | | |
| 432 | All O(1) Data Structure | | Hard |
| 431 | | | |
| 430 | | | |
| 429 | | | |
| 428 | | | |
| 427 | | | |
| 426 | | | |
| 425 | Word Squares | 🔒 | Hard |
| 424 | Longest Repeating Character Replacement | | Medium |
| 423 | Reconstruct Original Digits from English | | Medium |
| 422 | Valid Word Square | 🔒 | Easy |
| 421 | Maximum XOR of Two Numbers in an Array | | Medium |
| 420 | Strong Password Checker | | Hard |
| 419 | Battleships in a Board | | Medium |
| 418 | Sentence Screen Fitting | 🔒 | Medium |
| 417 | Pacific Atlantic Water Flow | | Medium |
| 416 | Partition Equal Subset Sum | | Medium |
| 415 | Add Strings | | Easy |
| 414 | Third Maximum Number | | Easy |
| 413 | Arithmetic Slices | | Medium |
| 412 | Fizz Buzz | Ruby | Easy |
| 411 | Minimum Unique Word Abbreviation | 🔒 | Hard |
| 410 | Split Array Largest Sum | | Hard |
| 409 | Longest Palindrome | Ruby | Easy |
| 408 | Valid Word Abbreviation | 🔒 | Easy |
| 407 | Trapping Rain Water II | | Hard |
| 406 | Queue Reconstruction by Height | | Medium |
| 405 | Convert a Number to Hexadecimal | Ruby | Easy |
| 404 | Sum of Left Leaves | Ruby | Easy |
| 403 | Frog Jump | | Hard |
| 402 | Remove K Digits | | Medium |
| 401 | Binary Watch | | Easy |
| 400 | Nth Digit | | Easy |
| 399 | Evaluate Division | | Medium |
| 398 | Random Pick Index | 🔜 | Medium |
| 397 | Integer Replacement | | Medium |
| 396 | Rotate Function | Ruby | Easy |
| 395 | Longest Substring with At Least K Repeating Characters | | Medium |
| 394 | Decode String | Ruby | Medium |
| 393 | UTF-8 Validation | Ruby | Medium |
| 392 | Is Subsequence | | Medium |
| 391 | Perfect Rectangle | | Hard |
| 390 | Elimination Game | | Medium |
| 389 | Find the Difference | Ruby | Easy |
| 388 | Longest Absolute File Path | | Medium |
| 387 | First Unique Character in a String | Ruby | Easy |
| 386 | Lexicographical Numbers | 🔜 | Medium |
| 385 | Mini Parser | Ruby | Medium |
| 384 | Shuffle an Array | 🔜 | Medium |
| 383 | Ransom Note | Ruby | Easy |
| 382 | Linked List Random Node | 🔜 | Medium |
| 381 | Insert Delete GetRandom O(1) - Duplicates allowed | 🔜 | Hard |
| 380 | Insert Delete GetRandom O(1) | 🔜 | Hard |
| 379 | Design Phone Directory | 🔒 | Medium |
| 378 | Kth Smallest Element in a Sorted Matrix | | Medium |
| 377 | Combination Sum IV | | Medium |
| 376 | Wiggle Subsequence | | Medium |
| 375 | Guess Number Higher or Lower II | | Medium |
| 374 | Guess Number Higher or Lower | 🔜 | Easy |
| 373 | Find K Pairs with Smallest Sums | | Medium |
| 372 | Super Pow | | Medium |
| 371 | Sum of Two Integers | Ruby | Easy |
| 370 | Range Addition | 🔒 | Medium |
| 369 | Plus One Linked List | 🔒 | Medium |
| 368 | Largest Divisible Subset | | Medium |
| 367 | Valid Perfect Square | Ruby | Easy |
| 366 | Find Leaves of Binary Tree | 🔒 | Medium |
| 365 | Water and Jug Problem | | Medium |
| 364 | Nested List Weight Sum II | 🔒 | Medium |
| 363 | Max Sum of Rectangle No Larger Than K | | Hard |
| 362 | Design Hit Counter | 🔒 | Medium |
| 361 | Bomb Enemy | 🔒 | Medium |
| 360 | Sort Transformed Array | 🔒 | Medium |
| 359 | Logger Rate Limiter | 🔒 | Easy |
| 358 | Rearrange String k Distance Apart | 🔒 | Hard |
| 357 | Count Numbers with Unique Digits | | Medium |
| 356 | Line Reflection | 🔒 | Medium |
| 355 | Design Twitter | 🔜 | Medium |
| 354 | Russian Doll Envelopes | | Hard |
| 353 | Design Snake Game | 🔒 | Medium |
| 352 | Data Stream as Disjoint Intervals | 🔜 | Hard |
| 351 | Android Unlock Patterns | 🔒 | Medium |
| 350 | Intersection of Two Arrays II | Ruby | Easy |
| 349 | Intersection of Two Arrays | Ruby | Easy |
| 348 | Design Tic-Tac-Toe | 🔒 | Medium |
| 347 | Top K Frequent Elements | Ruby | Medium |
| 346 | Moving Average from Data Stream | 🔒 | Easy |
| 345 | Reverse Vowels of a String | Ruby | Easy |
| 344 | Reverse String | Ruby | Easy |
| 343 | Integer Break | Ruby | Medium |
| 342 | Power of Four | Ruby | Easy |
| 341 | Flatten Nested List Iterator | 🔒 | Medium |
| 340 | Longest Substring with At Most K Distinct Characters | 🔒 | Hard |
| 339 | Nested List Weight Sum | 🔒 | Easy |
| 338 | Counting Bits | Ruby | Medium |
| 337 | House Robber III | Ruby | Medium |
| 336 | Palindrome Pairs | Ruby | Hard |
| 335 | Self Crossing | Ruby | Medium |
| 334 | Increasing Triplet Subsequence | Ruby | Medium |
| 333 | Largest BST Subtree | 🔒 | Medium |
| 332 | Reconstruct Itinerary | Ruby | Medium |
| 331 | Verify Preorder Serialization of a Binary Tree | Ruby | Medium |
| 330 | Patching Array | Ruby | Medium |
| 329 | Longest Increasing Path in a Matrix | Ruby | Medium |
| 328 | Odd Even Linked List | Ruby | Easy |
| 327 | Count of Range Sum | Ruby | Hard |
| 326 | Power of Three | Ruby | Easy |
| 325 | Maximum Size Subarray Sum Equals k | 🔒 | Easy |
| 324 | Wiggle Sort II | Ruby | Medium |
| 323 | Number of Connected Components in an Undirected Graph | 🔒 | Easy |
| 322 | Coin Change | Ruby | Medium |
| 321 | Create Maximum Number | Ruby | Hard |
| 320 | Generalized Abbreviation | 🔒 | Medium |
| 319 | Bulb Switcher | Ruby | Medium |
| 318 | Maximum Product of Word Lengths | Ruby | Medium |
| 317 | Shortest Distance from All Buildings | 🔒 | Hard |
| 316 | Remove Duplicate Letters | Ruby | Medium |
| 315 | Count of Smaller Numbers After Self | Ruby | Hard |
| 314 | Binary Tree Vertical Order Traversal | 🔒 | Medium |
| 313 | Super Ugly Number | Ruby | Medium |
| 312 | Burst Balloons | Ruby | Medium |
| 311 | Sparse Matrix Multiplication | 🔒 | Medium |
| 310 | Minimum Height Trees | Ruby | Medium |
| 309 | Best Time to Buy and Sell Stock with Cooldown | Ruby | Medium |
| 308 | Range Sum Query 2D - Mutable | 🔒 | Hard |
| 307 | Range Sum Query - Mutable | Ruby | Medium |
| 306 | Additive Number | Ruby | Medium |
| 305 | Number of Islands II | 🔒 | Hard |
| 304 | Range Sum Query 2D - Immutable | Ruby | Medium |
| 303 | Range Sum Query - Immutable | Ruby | Easy |
| 302 | Smallest Rectangle Enclosing Black Pixels | 🔒 | Medium |
| 301 | Remove Invalid Parentheses | Ruby | Medium |
| 300 | Longest Increasing Subsequence | Ruby | Medium |
| 299 | Bulls and Cows | Ruby | Easy |
| 298 | Binary Tree Longest Consecutive Sequence | 🔒 | Medium |
| 297 | Serialize and Deserialize Binary Tree | Ruby | Medium |
| 296 | Best Meeting Point | 🔒 | Medium |
| 295 | Find Median from Data Stream | Ruby | Hard |
| 294 | Flip Game II | 🔒 | Medium |
| 293 | Flip Game | 🔒 | Easy |
| 292 | Nim Game | Ruby | Easy |
| 291 | Word Pattern II | 🔒 | Hard |
| 290 | Word Pattern | Ruby | Easy |
| 289 | Game of Life | Ruby | Medium |
| 288 | Unique Word Abbreviation | 🔒 | Easy |
| 287 | Find the Duplicate Number | Ruby | Hard |
| 286 | Walls and Gates | 🔒 | Medium |
| 285 | Inorder Successor in BST | 🔒 | Medium |
| 284 | Peeking Iterator | 🔜 | Medium |
| 283 | Move Zeroes | Ruby | Easy |
| 282 | Expression Add Operators | Ruby | Hard |
| 281 | Zigzag Iterator | 🔒 | Medium |
| 280 | Wiggle Sort | 🔒 | Medium |
| 279 | Perfect Squares | Ruby | Medium |
| 278 | First Bad Version | Ruby | Easy |
| 277 | Find the Celebrity | 🔒 | Medium |
| 276 | Paint Fence | 🔒 | Easy |
| 275 | H-Index II | Ruby | Medium |
| 274 | H-Index | Ruby | Medium |
| 273 | Integer to English Words | Ruby | Medium |
| 272 | Closest Binary Search Tree Value II | 🔒 | Hard |
| 271 | Encode and Decode Strings | 🔒 | Medium |
| 270 | Closest Binary Search Tree Value | 🔒 | Easy |
| 269 | Alien Dictionary | 🔒 | Hard |
| 268 | Missing Number | Ruby | Medium |
| 267 | Palindrome Permutation II | 🔒 | Medium |
| 266 | Palindrome Permutation | 🔒 | Easy |
| 265 | Paint House II | 🔒 | Hard |
| 264 | Ugly Number II | Ruby | Medium |
| 263 | Ugly Number | Ruby | Easy |
| 262 | Trips and Users | MySQL | Hard |
| 261 | Graph Valid Tree | 🔒 | Medium |
| 260 | Single Number III | Ruby | Medium |
| 259 | 3Sum Smaller | 🔒 | Medium |
| 258 | Add Digits | Ruby | Easy |
| 257 | Binary Tree Paths | Ruby | Easy |
| 256 | Paint House | 🔒 | Medium |
| 255 | Verify Preorder Sequence in Binary Search Tree | 🔒 | Medium |
| 254 | Factor Combinations | 🔒 | Medium |
| 253 | Meeting Rooms II | 🔒 | Medium |
| 252 | Meeting Rooms | 🔒 | Easy |
| 251 | Flatten 2D Vector | 🔒 | Medium |
| 250 | Count Univalue Subtrees | 🔒 | Medium |
| 249 | Group Shifted Strings | 🔒 | Easy |
| 248 | Strobogrammatic Number III | 🔒 | Hard |
| 247 | Strobogrammatic Number II | 🔒 | Medium |
| 246 | Strobogrammatic Number | 🔒 | Easy |
| 245 | Shortest Word Distance III | 🔒 | Medium |
| 244 | Shortest Word Distance II | 🔒 | Medium |
| 243 | Shortest Word Distance | 🔒 | Easy |
| 242 | Valid Anagram | Ruby | Easy |
| 241 | Different Ways to Add Parentheses | Ruby | Medium |
| 240 | Search a 2D Matrix II | Ruby | Medium |
| 239 | Sliding Window Maximum | Ruby | Hard |
| 238 | Product of Array Except Self | Ruby | Medium |
| 237 | Delete Node in a Linked List | Ruby | Easy |
| 236 | Lowest Common Ancestor of a Binary Tree | Ruby | Medium |
| 235 | Lowest Common Ancestor of a Binary Search Tree | Ruby | Easy |
| 234 | Palindrome Linked List | Ruby | Easy |
| 233 | Number of Digit One | Ruby | Medium |
| 232 | Implement Queue using Stacks | Ruby | Easy |
| 231 | Power of Two | Ruby | Easy |
| 230 | Kth Smallest Element in a BST | Ruby | Medium |
| 229 | Majority Element II | Ruby | Medium |
| 228 | Summary Ranges | Ruby | Easy |
| 227 | Basic Calculator II | Ruby | Medium |
| 226 | Invert Binary Tree | Ruby | Easy |
| 225 | Implement Stack using Queues | Ruby | Easy |
| 224 | Basic Calculator | Ruby | Medium |
| 223 | Rectangle Area | Ruby | Easy |
| 222 | Count Complete Tree Nodes | Ruby | Medium |
| 221 | Maximal Square | Ruby | Medium |
| 220 | Contains Duplicate III | Ruby | Medium |
| 219 | Contains Duplicate II | Ruby | Easy |
| 218 | The Skyline Problem | Ruby | Hard |
| 217 | Contains Duplicate | Ruby | Easy |
| 216 | Combination Sum III | Ruby | Medium |
| 215 | Kth Largest Element in an Array | Ruby | Medium |
| 214 | Shortest Palindrome | Ruby | Hard |
| 213 | House Robber II | Ruby | Medium |
| 212 | Word Search II | Ruby | Hard |
| 211 | Add and Search Word - Data structure design | Ruby | Medium |
| 210 | Course Schedule II | Ruby | Medium |
| 209 | Minimum Size Subarray Sum | Ruby | Medium |
| 208 | Implement Trie (Prefix Tree) | Ruby | Medium |
| 207 | Course Schedule | Ruby | Medium |
| 206 | Reverse Linked List | Ruby | Easy |
| 205 | Isomorphic Strings | Ruby | Easy |
| 204 | Count Primes | Ruby | Easy |
| 203 | Remove Linked List Elements | Ruby | Easy |
| 202 | Happy Number | Ruby | Easy |
| 201 | Bitwise AND of Numbers Range | Ruby | Medium |
| 200 | Number of Islands | Ruby | Medium |
| 199 | Binary Tree Right Side View | Ruby | Medium |
| 198 | House Robber | Ruby | Easy |
| 197 | Rising Temperature | MySQL | Easy |
| 196 | Delete Duplicate Emails | MySQL | Easy |
| 195 | Tenth Line | Bash | Easy |
| 194 | Transpose File | Bash | Medium |
| 193 | Valid Phone Numbers | Bash | Easy |
| 192 | Word Frequency | Bash | Medium |
| 191 | Number of 1 Bits | Ruby | Easy |
| 190 | Reverse Bits | Ruby | Easy |
| 189 | Rotate Array | Ruby | Easy |
| 188 | Best Time to Buy and Sell Stock IV | Ruby | Hard |
| 187 | Repeated DNA Sequences | Ruby | Medium |
| 186 | Reverse Words in a String II | 🔒 | Medium |
| 185 | Department Top Three Salaries | MySQL | Hard |
| 184 | Department Highest Salary | MySQL | Medium |
| 183 | Customers Who Never Order | MySQL | Easy |
| 182 | Duplicate Emails | MySQL | Easy |
| 181 | Employees Earning More Than Their Managers | MySQL | Easy |
| 180 | Consecutive Numbers | MySQL | Medium |
| 179 | Largest Number | Ruby | Medium |
| 178 | Rank Scores | MySQL | Medium |
| 177 | Nth Highest Salary | MySQL | Medium |
| 176 | Second Highest Salary | MySQL | Easy |
| 175 | Combine Two Tables | MySQL | Easy |
| 174 | Dungeon Game | Ruby | Hard |
| 173 | Binary Search Tree Iterator | Ruby | Medium |
| 172 | Factorial Trailing Zeroes | Ruby | Easy |
| 171 | Excel Sheet Column Number | Ruby | Easy |
| 170 | Two Sum III - Data structure design | 🔒 | Easy |
| 169 | Majority Element | Ruby | Easy |
| 168 | Excel Sheet Column Title | Ruby | Easy |
| 167 | Two Sum II - Input array is sorted | 🔒 | Medium |
| 166 | Fraction to Recurring Decimal | Ruby | Medium |
| 165 | Compare Version Numbers | Ruby | Easy |
| 164 | Maximum Gap | Ruby | Hard |
| 163 | Missing Ranges | 🔒 | Medium |
| 162 | Find Peak Element | Ruby | Medium |
| 161 | One Edit Distance | 🔒 | Medium |
| 160 | Intersection of Two Linked Lists | 🔜 | Easy |
| 159 | Longest Substring with At Most Two Distinct Characters | 🔒 | Hard |
| 158 | Read N Characters Given Read4 II - Call multiple times | 🔒 | Hard |
| 157 | Read N Characters Given Read4 | 🔒 | Easy |
| 156 | Binary Tree Upside Down | 🔒 | Medium |
| 155 | Min Stack | Ruby | Easy |
| 154 | Find Minimum in Rotated Sorted Array II | Ruby | Hard |
| 153 | Find Minimum in Rotated Sorted Array | Ruby | Medium |
| 152 | Maximum Product Subarray | Ruby | Medium |
| 151 | Reverse Words in a String | 🔜 | Medium |
| 150 | Evaluate Reverse Polish Notation | Ruby | Medium |
| 149 | Max Points on a Line | Ruby | Hard |
| 148 | Sort List | Ruby | Medium |
| 147 | Insertion Sort List | Ruby | Medium |
| 146 | LRU Cache | Ruby | Hard |
| 145 | Binary Tree Postorder Traversal | Ruby | Hard |
| 144 | Binary Tree Preorder Traversal | Ruby | Medium |
| 143 | Reorder List | Ruby | Medium |
| 142 | Linked List Cycle II | 🔜 | Medium |
| 141 | Linked List Cycle | 🔜 | Medium |
| 140 | Word Break II | Ruby | Hard |
| 139 | Word Break | Ruby | Medium |
| 138 | Copy List with Random Pointer | 🔜 | Hard |
| 137 | Single Number II | Ruby | Medium |
| 136 | Single Number | Ruby | Medium |
| 135 | Candy | Ruby | Hard |
| 134 | Gas Station | Ruby | Medium |
| 133 | Clone Graph | 🔜 | Medium |
| 132 | Palindrome Partitioning II | Ruby | Hard |
| 131 | Palindrome Partitioning | Ruby | Medium |
| 130 | Surrounded Regions | Ruby | Medium |
| 129 | Sum Root to Leaf Numbers | Ruby | Medium |
| 128 | Longest Consecutive Sequence | Ruby | Hard |
| 127 | Word Ladder | Ruby | Medium |
| 126 | Word Ladder II | 🔜 | Hard |
| 125 | Valid Palindrome | Ruby | Easy |
| 124 | Binary Tree Maximum Path Sum | Ruby | Hard |
| 123 | Best Time to Buy and Sell Stock III | Ruby | Hard |
| 122 | Best Time to Buy and Sell Stock II | Ruby | Medium |
| 121 | Best Time to Buy and Sell Stock | Ruby | Medium |
| 120 | Triangle | Ruby | Medium |
| 119 | Pascal's Triangle II | Ruby | Easy |
| 118 | Pascal's Triangle | Ruby | Easy |
| 117 | Populating Next Right Pointers in Each Node II | 🔜 | Hard |
| 116 | Populating Next Right Pointers in Each Node | 🔜 | Medium |
| 115 | Distinct Subsequences | Ruby | Hard |
| 114 | Flatten Binary Tree to Linked List | Ruby | Medium |
| 113 | Path Sum II | Ruby | Medium |
| 112 | Path Sum | Ruby | Easy |
| 111 | Minimum Depth of Binary Tree | Ruby | Easy |
| 110 | Balanced Binary Tree | Ruby | Easy |
| 109 | Convert Sorted List to Binary Search Tree | Ruby | Medium |
| 108 | Convert Sorted Array to Binary Search Tree | Ruby | Medium |
| 107 | Binary Tree Level Order Traversal II | Ruby | Easy |
| 106 | Construct Binary Tree from Inorder and Postorder Traversal | Ruby | Medium |
| 105 | Construct Binary Tree from Preorder and Inorder Traversal | Ruby | Medium |
| 104 | Maximum Depth of Binary Tree | Ruby | Easy |
| 103 | Binary Tree Zigzag Level Order Traversal | Ruby | Medium |
| 102 | Binary Tree Level Order Traversal | Ruby | Easy |
| 101 | Symmetric Tree | Ruby | Easy |
| 100 | Same Tree | Ruby | Easy |
| 99 | Recover Binary Search Tree | Ruby | Hard |
| 98 | Validate Binary Search Tree | Ruby | Medium |
| 97 | Interleaving String | Ruby | Hard |
| 96 | Unique Binary Search Trees | Ruby | Medium |
| 95 | Unique Binary Search Trees II | Ruby | Medium |
| 94 | Binary Tree Inorder Traversal | Ruby | Medium |
| 93 | Restore IP Addresses | Ruby | Medium |
| 92 | Reverse Linked List II | Ruby | Medium |
| 91 | Decode Ways | Ruby | Medium |
| 90 | Subsets II | Ruby | Medium |
| 89 | Gray Code | Ruby | Medium |
| 88 | Merge Sorted Array | Ruby | Easy |
| 87 | Scramble String | Ruby | Hard |
| 86 | Partition List | Ruby | Medium |
| 85 | Maximal Rectangle | Ruby | Hard |
| 84 | Largest Rectangle in Histogram | Ruby | Hard |
| 83 | Remove Duplicates from Sorted List | Ruby | Easy |
| 82 | Remove Duplicates from Sorted List II | Ruby | Medium |
| 81 | Search in Rotated Sorted Array II | Ruby | Medium |
| 80 | Remove Duplicates from Sorted Array II | Ruby | Medium |
| 79 | Word Search | Ruby | Medium |
| 78 | Subsets | Ruby | Medium |
| 77 | Combinations | Ruby | Medium |
| 76 | Minimum Window Substring | Ruby | Hard |
| 75 | Sort Colors | Ruby | Medium |
| 74 | Search a 2D Matrix | Ruby | Medium |
| 73 | Set Matrix Zeroes | Ruby | Medium |
| 72 | Edit Distance | Ruby | Hard |
| 71 | Simplify Path | Ruby | Medium |
| 70 | Climbing Stairs | Ruby | Easy |
| 69 | Sqrt() | Ruby | Medium |
| 68 | Text Justification | Ruby | Hard |
| 67 | Add Binary | Ruby | Easy |
| 66 | Plus One | Ruby | Easy |
| 65 | Valid Number | Ruby | Hard |
| 64 | Minimum Path Sum | Ruby | Medium |
| 63 | Unique Paths II | Ruby | Medium |
| 62 | Unique Paths | Ruby | Medium |
| 61 | Rotate List | Ruby | Medium |
| 60 | Permutation Sequence | Ruby | Medium |
| 59 | Spiral Matrix II | Ruby | Medium |
| 58 | Length of Last Word | Ruby | Easy |
| 57 | Insert Interval | Ruby | Hard |
| 56 | Merge Intervals | Ruby | Hard |
| 55 | Jump Game | Ruby | Medium |
| 54 | Spiral Matrix | Ruby | Medium |
| 53 | Maximum Subarray | Ruby | Medium |
| 52 | N-Queens II | Ruby | Hard |
| 51 | N-Queens | Ruby | Hard |
| 50 | Pow(x, n) | Ruby | Medium |
| 49 | Group Anagrams | Ruby | Medium |
| 48 | Rotate Image | Ruby | Medium |
| 47 | Permutations II | Ruby | Medium |
| 46 | Permutations | Ruby | Medium |
| 45 | Jump Game II | Ruby | Hard |
| 44 | Wildcard Matching | Ruby | Hard |
| 43 | Multiply Strings | Ruby | Medium |
| 42 | Trapping Rain Water | Ruby | Hard |
| 41 | First Missing Positive | Ruby | Hard |
| 40 | Combination Sum II | Ruby | Medium |
| 39 | Combination Sum | Ruby | Medium |
| 38 | Count and Say | Ruby | Easy |
| 37 | Sudoku Solver | Ruby | Hard |
| 36 | Valid Sudoku | Ruby | Easy |
| 35 | Search Insert Position | Ruby | Medium |
| 34 | Search for a Range | Ruby | Medium |
| 33 | Search in Rotated Sorted Array | Ruby | Hard |
| 32 | Longest Valid Parentheses | Ruby | Hard |
| 31 | Next Permutation | Ruby | Medium |
| 30 | Substring with Concatenation of All Words | Ruby | Hard |
| 29 | Divide Two Integers | Ruby | Medium |
| 28 | Implement strStr() | Ruby | Easy |
| 27 | Remove Element | Ruby | Easy |
| 26 | Remove Duplicates from Sorted Array | Ruby | Easy |
| 25 | Reverse Nodes in k-Group | Ruby | Hard |
| 24 | Swap Nodes in Pairs | Ruby | Medium |
| 23 | Merge k Sorted Lists | Ruby | Hard |
| 22 | Generate Parentheses | Ruby | Medium |
| 21 | Merge Two Sorted Lists | Ruby | Easy |
| 20 | Valid Parentheses | Ruby | Easy |
| 19 | Remove Nth Node From End of List | Ruby | Easy |
| 18 | 4Sum | Ruby | Medium |
| 17 | Letter Combinations of a Phone Number | Ruby | Medium |
| 16 | 3Sum Closest | Ruby | Medium |
| 15 | 3Sum | Ruby | Medium |
| 14 | Longest Common Prefix | Ruby | Easy |
| 13 | Roman to Integer | Ruby | Easy |
| 12 | Integer to Roman | Ruby | Medium |
| 11 | Container With Most Water | Ruby | Medium |
| 10 | Regular Expression Matching | Ruby | Hard |
| 9 | Palindrome Number | Ruby | Easy |
| 8 | String to Integer (atoi) | Ruby | Easy |
| 7 | Reverse Integer | Ruby | Easy |
| 6 | ZigZag Conversion | Ruby | Easy |
| 5 | Longest Palindromic Substring | Ruby | Medium |
| 4 | Median of Two Sorted Arrays | Ruby | Hard |
| 3 | Longest Substring Without Repeating Characters | Ruby | Medium |
| 2 | Add Two Numbers | Ruby | Medium |
| 1 | Two Sum | Ruby | Medium |