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LeetCode Pattern 500 offers 500 solutions for LeetCode problems in Python and Java, 17 notes on essential concepts related to data structures and algorithms, and 130 patterns for solving LeetCode problems.

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Name		Name	Last commit message	Last commit date
Latest commit History 174 Commits
[A]tree		[A]tree
[B]linked-list		[B]linked-list
[C]hashmap		[C]hashmap
[D]binary-search		[D]binary-search
[E]heap		[E]heap
[F]string		[F]string
[G]trie		[G]trie
[H]array		[H]array
[I]stack-queue		[I]stack-queue
[J]backtracking		[J]backtracking
[K]graph		[K]graph
[L]bit-manipulation		[L]bit-manipulation
[M]dynamic-programming		[M]dynamic-programming
[N]greedy		[N]greedy
[O]math		[O]math
[P]segment-tree		[P]segment-tree
[Q]basic		[Q]basic
.gitignore		.gitignore
LICENSE		LICENSE
README.md		README.md

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LeetCode Pattern 500

If you often find yourself grappling with how to tackle LeetCode problems, our repo is here to assist you!

LeetCode Pattern 500 is meticulously designed to facilitate your swift adaptation to diverse problem types and their numerous variations by discerning recurring patterns within these problems.

What is LeetCode Pattern 500

LeetCode Pattern 500 is inspired by Blind 75 and Grind 75's classic problem selection. LeetCode Pattern 500 offers 500 solutions for LeetCode problems in Python and Java, 17 notes on essential concepts related to data structures and algorithms, and 130 patterns for solving LeetCode problems. Most importantly, each solution provides analysis of which pattern to be used and the time/space complexity. This comprehensive resource can help you improve your coding skills, deepen your understanding of fundamental DSA topics, and prepare for SDE interviews.

Mind map for all 130 patterns in LeetCode Pattern 500

Check ourmind map in Figma.

Suggestions & Questions

Feel free to raise issues or post in discussions.

LeetCode Pattern 500

Num	Grind 75	Name	Topic	Pattern	Solution
001		`tree note`	[A]tree
002	O	100. Same Tree	[A]tree-divide-and-conquer	two branch top-down	Python Java
003	O	101. Symmetric Tree	[A]tree-divide-and-conquer	two branch top-down	Python Java
004	O	98. Validate Binary Search Tree	[A]tree-divide-and-conquer	two branch top-down	Python Java
005	O	105. Construct Binary Tree from Preorder and Inorder Traversal	[A]tree-divide-and-conquer	re-build tree (top-down)	Python Java
006		106. Construct Binary Tree from Inorder and Postorder Traversal	[A]tree-divide-and-conquer	re-build tree (top-down)	Python Java
007		889. Construct Binary Tree from Preorder and Postorder Traversal	[A]tree-divide-and-conquer	re-build tree (top-down)	Python
008		1008. Construct Binary Search Tree from Preorder Traversal	[A]tree-divide-and-conquer	re-build BST (top-down approach)	Python
009	O	108. Convert Sorted Array to Binary Search Tree	[A]tree-divide-and-conquer	re-build BST (top-down approach)	Python Java
010		109. Convert Sorted List to Binary Search Tree	[A]tree-divide-and-conquer	re-build BST (inorder approach)	Python
011		700. Search in a Binary Search Tree	[A]tree-divide-and-conquer	use BST attributes	Python
012		701. Insert into a Binary Search Tree	[A]tree-divide-and-conquer	use BST attributes	Python
013	O	285. Inorder Successor in BST	[A]tree-divide-and-conquer	use BST attributes	Python
014		450. Delete Node in a BST	[A]tree-divide-and-conquer	use BST attributes	Python
015	O	235. Lowest Common Ancestor of a Binary Search Tree	[A]tree-divide-and-conquer	find LCA	Python Java
016		1650. Lowest Common Ancestor of a Binary Tree III	[A]tree-divide-and-conquer	find LCA	Python
017		116. Populating Next Right Pointers in Each Node	[A]tree-divide-and-conquer	populate next ptr	Python
018		117. Populating Next Right Pointers in Each Node II	[A]tree-divide-and-conquer	populate next ptr	Python
019		96. Unique Binary Search Trees	[A]tree-divide-and-conquer	unique BST	Python
020		95. Unique Binary Search Trees II	[A]tree-divide-and-conquer	unique BST	Python
021		872. Leaf-Similar Trees	[A]tree-dfs-preorder	preorder	Python
022	O	226. Invert Binary Tree	[A]tree-dfs-preorder	preorder	Python Java
023		1448. Count Good Nodes in Binary Tree	[A]tree-dfs-preorder	preorder	Python
024		1457. Pseudo-Palindromic Paths in a Binary Tree	[A]tree-dfs-preorder	preorder	Python
025	O	572. Subtree of Another Tree	[A]tree-dfs-preorder	turn tree to string	Python Java
026		606. Construct String from Binary Tree	[A]tree-dfs-preorder	turn tree to string	Python
027	O	297. Serialize and Deserialize Binary Tree	[A]tree-dfs-preorder	turn tree to string	Python
028		449. Serialize and Deserialize BST	[A]tree-dfs-preorder	turn tree to string	Python
029		545. Boundary of Binary Tree	[A]tree-dfs-preorder	record leaves	Python
030		94. Binary Tree Inorder Traversal	[A]tree-dfs-inorder	inorder	Python
031	O	230. Kth Smallest Element in a BST	[A]tree-dfs-inorder	inorder	Python Java
032		173. Binary Search Tree Iterator	[A]tree-dfs-inorder	inorder	Python
033		99. Recover Binary Search Tree	[A]tree-dfs-inorder	inorder	Python
034		366. Find Leaves of Binary Tree	[A]tree-dfs-postorder	postorder	Python
035	O	236. Lowest Common Ancestor of a Binary Tree	[A]tree-dfs-postorder	postorder	Python Java
036	O	124. Binary Tree Maximum Path Sum	[A]tree-dfs-postorder	postorder	Python
037	O	543. Diameter of Binary Tree	[A]tree-dfs-postorder	postorder	Python Java
038	O	110. Balanced Binary Tree	[A]tree-dfs-postorder	postorder	Python Java
039		865. Smallest Subtree with all the Deepest Nodes	[A]tree-dfs-postorder	postorder	Python
040		1120. Maximum Average Subtree	[A]tree-dfs-postorder	postorder	Python
041		298. Binary Tree Longest Consecutive Sequence	[A]tree-dfs-postorder	postorder	Python
042		1644. Lowest Common Ancestor of a Binary Tree II	[A]tree-dfs-postorder	postorder	Python
043		1145. Binary Tree Coloring Game	[A]tree-dfs-postorder	postorder	Python
044		2246. Longest Path With Different Adjacent Characters	[A]tree-dfs-postorder	postorder	Python
045	O	102. Binary Tree Level Order Traversal	[A]tree-bfs	bfs	Python Java
046	O	103. Binary Tree Zigzag Level Order Traversal	[A]tree-bfs	bfs	Python
047	O	199. Binary Tree Right Side View	[A]tree-bfs	bfs	Python Java
048	O	104. Maximum Depth of Binary Tree	[A]tree-bfs	bfs	Python Java
049		2415. Reverse Odd Levels of Binary Tree	[A]tree-bfs	bfs	Python
050		623. Add One Row to Tree	[A]tree-bfs	bfs	Python
051		690. Employee Importance	[A]tree-bfs	bfs	Python
052	O	863. All Nodes Distance K in Binary Tree	[A]tree-bfs	build a child_parent hashmap	Python
053		2385. Amount of Time for Binary Tree to Be Infected	[A]tree-bfs	build a child_parent hashmap	Python
054	O	662. Maximum Width of Binary Tree	[A]tree-bfs	assign idx	Python
055		314. Binary Tree Vertical Order Traversal	[A]tree-bfs	assign coordinates	Python
056		987. Vertical Order Traversal of a Binary Tree	[A]tree-bfs	assign coordinates	Python
057		`linked-list note`	[B]linked-list
058	O	21. Merge Two Sorted Lists	[B]linked-list	use sentinel node	Python Java
059	O	328. Odd Even Linked List	[B]linked-list	use sentinel node	Python
060	O	2. Add Two Numbers	[B]linked-list	use sentinel node	Python Java
061	O	19. Remove Nth Node From End of List	[B]linked-list	use sentinel node	Python
062		369. Plus One Linked List	[B]linked-list	use sentinel node	Python
063	O	141. Linked List Cycle	[B]linked-list	use two pointers (slow and fast)	Python Java
064		142. Linked List Cycle II	[B]linked-list	use two pointers (slow and fast)	Python
065	O	876. Middle of the Linked List	[B]linked-list	use two pointers (slow and fast)	Python Java
066	O	206. Reverse Linked List	[B]linked-list	use two pointers (prev and cur)	Python Java
067		92. Reverse Linked List II	[B]linked-list	use two pointers (prev and cur)	Python
068	O	25. Reverse Nodes in k-Group	[B]linked-list	use two pointers (prev and cur)	Python
069		2074. Reverse Nodes in Even Length Groups	[B]linked-list	use two pointers (prev and cur)	Python
070	O	24. Swap Nodes in Pairs	[B]linked-list	use two pointers (prev and cur)	Python
071		1836. Remove Duplicates From an Unsorted Linked List	[B]linked-list	use two pointers (prev and cur)	Python
072		83. Remove Duplicates from Sorted List	[B]linked-list	use two pointers (prev and cur)	Python
073		82. Remove Duplicates from Sorted List II	[B]linked-list	use two pointers (prev and cur)	Python
074		160. Intersection of Two Linked Lists	[B]linked-list	use two pointers (find LCA/intersection)	Python
075	O	234. Palindrome Linked List	[B]linked-list	use two pointers (utilize symmetry property)	Python Java
076	O	143. Reorder List	[B]linked-list	use two pointers (utilize symmetry property)	Python
077		2130. Maximum Twin Sum of a Linked List	[B]linked-list	use two pointers (utilize symmetry property)	Python
078	O	61. Rotate List	[B]linked-list	get linked list length	Python
079		1019. Next Greater Node In Linked List	[B]linked-list	get linked list length	Python
080	O	148. Sort List	[B]linked-list	use merge sort to sort list	Python
081		138. Copy List with Random Pointer	[B]linked-list	interweaving nodes	Python
082	O	146. LRU Cache	[B]linked-list	use dll and hashmap together	Python Java
083		460. LFU Cache	[B]linked-list	use dll and hashmap together	Python
084		432. All O`one Data Structure	[B]linked-list	use dll and hashmap together	Python
085		237. Delete Node in a Linked List	[B]linked-list	change val as change node	Python
086		1206. Design Skiplist	[B]linked-list	skiplist	Python
087		`hashmap note`	[C]hashmap
088		705. Design HashSet	[C]hashmap	separate chaining	Python
089		706. Design HashMap	[C]hashmap	separate chaining	Python
090		1805. Number of Different Integers in a String	[C]hashmap	store val	Python
091	O	217. Contains Duplicate	[C]hashmap	store val	Python Java
092	O	128. Longest Consecutive Sequence	[C]hashmap	store val	Python Java
093	O	13. Roman to Integer	[C]hashmap	store val	Python Java
094		953. Verifying an Alien Dictionary	[C]hashmap	store val	Python
095		2342. Max Sum of a Pair With Equal Sum of Digits	[C]hashmap	store val	Python
096	O	336. Palindrome Pairs	[C]hashmap	store val	Python
097	O	1. Two Sum	[C]hashmap	store val	Python Java
098	O	380. Insert Delete GetRandom O(1)	[C]hashmap	store val	Python
099		381. Insert Delete GetRandom O(1) - Duplicates allowed	[C]hashmap	store val	Python
100		734. Sentence Similarity	[C]hashmap	store val	Python
101		609. Find Duplicate File in System	[C]hashmap	store val	Python
102		249. Group Shifted Strings	[C]hashmap	store val	Python
103	O	383. Ransom Note	[C]hashmap	store sth’s freq	Python Java
104	O	242. Valid Anagram	[C]hashmap	store sth’s freq	Python Java
105	O	409. Longest Palindrome	[C]hashmap	store sth’s freq	Python Java
106		387. First Unique Character in a String	[C]hashmap	store sth’s freq	Python Java
107		767. Reorganize String	[C]hashmap	store sth’s freq	Python
108		266. Palindrome Permutation	[C]hashmap	store sth’s freq	Python
109		2423. Remove Letter To Equalize Frequency	[C]hashmap	store sth’s freq	Python
110		299. Bulls and Cows	[C]hashmap	store sth’s freq	Python
111		819. Most Common Word	[C]hashmap	store sth’s freq	Python
112	O	49. Group Anagrams	[C]hashmap	store sth’s freq	Python Java
113		1152. Analyze User Website Visit Pattern	[C]hashmap	store sth’s freq	Python
114		828. Count Unique Characters of All Substrings of a Given String	[C]hashmap	snapshot of hashmap	Python
115		1055. Shortest Way to Form String	[C]hashmap	snapshot of hashmap	Python
116		205. Isomorphic Strings	[C]hashmap	build bijection mapping relation	Python Java
117		890. Find and Replace Pattern	[C]hashmap	build bijection mapping relation	Python
118		1010. Pairs of Songs With Total Durations Divisible by 60	[C]hashmap	store valid val’s freq for finding pairs	Python
119		2364. Count Number of Bad Pairs	[C]hashmap	store valid val’s freq for finding pairs	Python
120		2013. Detect Squares	[C]hashmap	store valid val’s freq for finding pairs	Python
121		`binary-search note`	[D]binary-search
122	O	704. Binary Search	[D]binary-search	search in a sorted array for specific val	Python Java
123		367. Valid Perfect Square	[D]binary-search	search in a sorted array for specific val	Python
124	O	74. Search a 2D Matrix	[D]binary-search	search in a sorted array for specific val	Python Java
125		34. Find First and Last Position of Element in Sorted Array	[D]binary-search	search in a sorted array for specific val	Python Java
126		702. Search in a Sorted Array of Unknown Size	[D]binary-search	search in a sorted array for specific val	Python
127		35. Search Insert Position	[D]binary-search	search in a sorted array for most close val	Python Java
128		1428. Leftmost Column with at Least a One	[D]binary-search	search in a sorted array for most close val	Python
129		744. Find Smallest Letter Greater Than Target	[D]binary-search	search in a sorted array for most close val	Python
130	O	981. Time Based Key-Value Store	[D]binary-search	search in a sorted array for most close val	Python Java
131	O	528. Random Pick with Weight	[D]binary-search	search in a sorted array for most close val	Python
132	O	278. First Bad Version	[D]binary-search	search in sth’s range	Python Java
133		222. Count Complete Tree Nodes	[D]binary-search	search in sth’s range	Python
134		878. Nth Magical Number	[D]binary-search	search in sth’s range	Python
135		1201. Ugly Number III	[D]binary-search	search in sth’s range	Python
136	O	4. Median of Two Sorted Arrays	[D]binary-search	search in sth’s range	Python
137		1062. Longest Repeating Substring	[D]binary-search	search in sth’s range	Python
138		1011. Capacity To Ship Packages Within D Days	[D]binary-search	search in sth’s range	Python
139		875. Koko Eating Bananas	[D]binary-search	search in sth’s range	Python
140		719. Find K-th Smallest Pair Distance	[D]binary-search	search in sth’s range	Python
141		852. Peak Index in a Mountain Array	[D]binary-search	use boundary to record	Python
142	O	658. Find K Closest Elements	[D]binary-search	use boundary to record	Python
143		162. Find Peak Element	[D]binary-search	use boundary to record	Python
144	O	33. Search in Rotated Sorted Array	[D]binary-search	rotated sorted array	Python Java
145		81. Search in Rotated Sorted Array II	[D]binary-search	rotated sorted array	Python
146	O	153. Find Minimum in Rotated Sorted Array	[D]binary-search	rotated sorted array	Python
147		`heap note`	[E]heap
148	O	1235. Maximum Profit in Job Scheduling	[E]heap	greedily schedule tasks (start/end/val)	Python
149		646. Maximum Length of Pair Chain	[E]heap	greedily schedule tasks (start/end/val)	Python
150		2008. Maximum Earnings From Taxi	[E]heap	greedily schedule tasks (start/end/val)	Python
151		2054. Two Best Non-Overlapping Events	[E]heap	greedily schedule tasks (start/end/val)	Python
152	O	973. K Closest Points to Origin	[E]heap	top k problem (based on heap)	Python Java
153	O	692. Top K Frequent Words	[E]heap	top k problem (based on heap)	Python
154		264. Ugly Number II	[E]heap	k way merge problem	Python
155		313. Super Ugly Number	[E]heap	k way merge problem	Python
156		355. Design Twitter	[E]heap	k way merge problem	Python
157	O	759. Employee Free Time	[E]heap	k way merge problem	Python
158	O	632. Smallest Range Covering Elements from K Lists	[E]heap	k way merge problem	Python
159	O	23. Merge k Sorted Lists	[E]heap	k way merge problem	Python
160	O	295. Find Median from Data Stream	[E]heap	two heap problem	Python
161		502. IPO	[E]heap	two heap problem	Python
162		480. Sliding Window Median	[E]heap	two heap problem	Python
163		1383. Maximum Performance of a Team	[E]heap	storing and popping out elements	Python
164		630. Course Schedule III	[E]heap	storing and popping out elements	Python
165		1094. Car Pooling	[E]heap	storing and popping out elements	Python
166		1705. Maximum Number of Eaten Apples	[E]heap	storing and popping out elements	Python
167		1792. Maximum Average Pass Ratio	[E]heap	storing and popping out elements	Python
168		378. Kth Smallest Element in a Sorted Matrix	[E]heap	use bfs and heap	Python
169		373. Find K Pairs with Smallest Sums	[E]heap	use bfs and heap	Python
170		407. Trapping Rain Water II	[E]heap	use bfs and heap	Python
171		`string note`	[F]string
172	O	844. Backspace String Compare	[F]string	traverse from end	Python Java
173		43. Multiply Strings	[F]string	traverse from end	Python
174		58. Length of Last Word	[F]string	traverse from end	Python
175	O	8. String to Integer (atoi)	[F]string	handle value’s bound	Python Java
176	O	271. Encode and Decode Strings	[F]string	use chunk	Python
177		28. Find the Index of the First Occurrence in a String	[F]string	use rabin karp (rolling hash)	Python
178		187. Repeated DNA Sequences	[F]string	use rabin karp (rolling hash)	Python
179		1044. Longest Duplicate Substring	[F]string	use rabin karp (rolling hash)	Python
180		718. Maximum Length of Repeated Subarray	[F]string	use rabin karp (rolling hash)	Python
181	O	14. Longest Common Prefix	[F]string	string composition	Python Java
182		273. Integer to English Words	[F]string	string composition	Python
183		68. Text Justification	[F]string	string composition	Python
184		65. Valid Number	[F]string	string composition	Python
185		6. Zigzag Conversion	[F]string	string composition	Python
186		`trie note`	[G]trie
187	O	208. Implement Trie (Prefix Tree)	[G]trie	standard trie	Python Java
188	O	588. Design In-Memory File System	[G]trie	custom trie node	Python
189		1268. Search Suggestions System	[G]trie	custom trie node	Python
190		2185. Counting Words With a Given Prefix	[G]trie	custom trie node	Python
191		2416. Sum of Prefix Scores of Strings	[G]trie	custom trie node	Python
192		745. Prefix and Suffix Search	[G]trie	custom trie node	Python
193		1166. Design File System	[G]trie	custom trie node	Python
194	O	211. Design Add and Search Words Data Structure	[G]trie	perform dfs inside trie	Python
195		472. Concatenated Words	[G]trie	perform dfs inside trie	Python
196		642. Design Search Autocomplete System	[G]trie	perform dfs inside trie	Python
197		`array note`	[H]array
198		243. Shortest Word Distance	[H]array	traverse	Python
199	O	169. Majority Element	[H]array	use boyer moore vote algorithm	Python Java
200		229. Majority Element II	[H]array	use boyer moore vote algorithm	Python
201	O	189. Rotate Array	[H]array	use reverse technique	Python
202	O	362. Design Hit Counter	[H]array	use circular array	Python
203	O	41. First Missing Positive	[H]array	specific range array (cyclic sort)	Python
204		442. Find All Duplicates in an Array	[H]array	specific range array (cyclic sort)	Python
205		448. Find All Numbers Disappeared in an Array	[H]array	specific range array (cyclic sort)	Python
206	O	287. Find the Duplicate Number	[H]array	specific range array (cycle detection)	Python
207		845. Longest Mountain in Array	[H]array	use finite state machine	Python
208		370. Range Addition	[H]array	use difference array	Python
209		849. Maximize Distance to Closest Person	[H]array	count continuous elements	Python
210		384. Shuffle an Array	[H]array	use knuth shuffle	Python
211		398. Random Pick Index	[H]array	use reservoir sampling	Python
212		1535. Find the Winner of an Array Game	[H]array	simulation	Python
213		280. Wiggle Sort	[H]array	use swap	Python
214		1472. Design Browser History	[H]array	maintain array's range dynamically	Python
215		163. Missing Ranges	[H]array	pre-process the array	Python
216	O	56. Merge Intervals	[H]array-line-sweep	compare two intervals each round	Python Java
217	O	57. Insert Interval	[H]array-line-sweep	compare two intervals each round	Python Java
218		1272. Remove Interval	[H]array-line-sweep	compare two intervals each round	Python
219	O	252. Meeting Rooms	[H]array-line-sweep	compare two intervals each round	Python Java
220	O	435. Non-overlapping Intervals	[H]array-line-sweep	compare two intervals each round	Python
221		1288. Remove Covered Intervals	[H]array-line-sweep	compare two intervals each round	Python
222		452. Minimum Number of Arrows to Burst Balloons	[H]array-line-sweep	compare two intervals each round	Python
223		757. Set Intersection Size At Least Two	[H]array-line-sweep	compare two intervals each round	Python
224		986. Interval List Intersections	[H]array-line-sweep	compare two intervals each round	Python
225		1229. Meeting Scheduler	[H]array-line-sweep	compare two intervals each round	Python
226	O	253. Meeting Rooms II	[H]array-line-sweep	use heap to store previous intervals’ states	Python
227		1851. Minimum Interval to Include Each Query	[H]array-line-sweep	use heap to store previous intervals’ states	Python
228		303. Range Sum Query - Immutable	[H]array-prefix-sum	use standard prefix sum	Python
229		304. Range Sum Query 2D - Immutable	[H]array-prefix-sum	use standard prefix sum	Python
230	O	238. Product of Array Except Self	[H]array-prefix-sum	use standard prefix sum	Python Java
231		724. Find Pivot Index	[H]array-prefix-sum	use standard prefix sum	Python
232		2256. Minimum Average Difference	[H]array-prefix-sum	use standard prefix sum	Python
233		2100. Find Good Days to Rob the Bank	[H]array-prefix-sum	use standard prefix sum	Python
234		2055. Plates Between Candles	[H]array-prefix-sum	use standard prefix sum	Python
235		1031. Maximum Sum of Two Non-Overlapping Subarrays	[H]array-prefix-sum	use standard prefix sum	Python
236	O	560. Subarray Sum Equals K	[H]array-prefix-sum	use hashmap to validate the gap subarray	Python Java
237	O	525. Contiguous Array	[H]array-prefix-sum	use hashmap to validate the gap subarray	Python
238		974. Subarray Sums Divisible by K	[H]array-prefix-sum	use hashmap to validate the gap subarray	Python
239		523. Continuous Subarray Sum	[H]array-prefix-sum	use hashmap to validate the gap subarray	Python
240		325. Maximum Size Subarray Sum Equals k	[H]array-prefix-sum	use hashmap to validate the gap subarray	Python
241		1248. Count Number of Nice Subarrays	[H]array-prefix-sum	use hashmap to validate the gap subarray	Python
242		363. Max Sum of Rectangle No Larger Than K	[H]array-prefix-sum	use hashmap to validate the gap subarray	Python
243		548. Split Array with Equal Sum	[H]array-prefix-sum	use hashmap to validate the gap subarray	Python
244	O	3. Longest Substring Without Repeating Characters	[H]array-sliding-window	use standard sliding window	Python Java
245		567. Permutation in String	[H]array-sliding-window	use standard sliding window	Python
246	O	438. Find All Anagrams in a String	[H]array-sliding-window	use standard sliding window	Python Java
247	O	424. Longest Repeating Character Replacement	[H]array-sliding-window	use standard sliding window	Python Java
248		1151. Minimum Swaps to Group All 1's Together	[H]array-sliding-window	use standard sliding window	Python
249		2134. Minimum Swaps to Group All 1's Together II	[H]array-sliding-window	use standard sliding window	Python
250		340. Longest Substring with At Most K Distinct Characters	[H]array-sliding-window	use standard sliding window	Python
251		1100. Find K-Length Substrings With No Repeated Characters	[H]array-sliding-window	use standard sliding window	Python
252		904. Fruit Into Baskets	[H]array-sliding-window	use standard sliding window	Python
253		1423. Maximum Points You Can Obtain from Cards	[H]array-sliding-window	use standard sliding window	Python
254		30. Substring with Concatenation of All Words	[H]array-sliding-window	use standard sliding window	Python
255		395. Longest Substring with At Least K Repeating Characters	[H]array-sliding-window	use standard sliding window	Python
256	O	76. Minimum Window Substring	[H]array-sliding-window	use shrink type sliding window	Python
257		209. Minimum Size Subarray Sum	[H]array-sliding-window	use shrink type sliding window	Python
258	O	121. Best Time to Buy and Sell Stock	[H]array-two-pointers-same-direction	use left ptr to record	Python Java
259		122. Best Time to Buy and Sell Stock II	[H]array-two-pointers-same-direction	use left ptr to record	Python
260	O	283. Move Zeroes	[H]array-two-pointers-same-direction	use left ptr to record	Python Java
261		27. Remove Element	[H]array-two-pointers-same-direction	use left ptr to record	Python
262		26. Remove Duplicates from Sorted Array	[H]array-two-pointers-same-direction	use left ptr to record	Python
263		80. Remove Duplicates from Sorted Array II	[H]array-two-pointers-same-direction	use left ptr to record	Python
264	O	75. Sort Colors	[H]array-two-pointers-same-direction	use left ptr to record	Python Java
265		2414. Length of the Longest Alphabetical Continuous Substring	[H]array-two-pointers-same-direction	use left ptr to record	Python
266	O	31. Next Permutation	[H]array-two-pointers-same-direction	find next permutation	Python
267		556. Next Greater Element III	[H]array-two-pointers-same-direction	find next permutation	Python
268		165. Compare Version Numbers	[H]array-two-pointers-same-direction	traverse two sequences	Python
269		2337. Move Pieces to Obtain a String	[H]array-two-pointers-same-direction	traverse two sequences	Python
270		1574. Shortest Subarray to be Removed to Make Array Sorted	[H]array-two-pointers-same-direction	traverse two sequences	Python
271		244. Shortest Word Distance II	[H]array-two-pointers-same-direction	traverse two sequences	Python
272		167. Two Sum II - Input Array Is Sorted	[H]array-two-pointers-opposite-direction	use shrink type	Python
273	O	15. 3Sum	[H]array-two-pointers-opposite-direction	use shrink type	Python Java
274		18. 4Sum	[H]array-two-pointers-opposite-direction	use shrink type	Python
275	O	16. 3Sum Closest	[H]array-two-pointers-opposite-direction	use shrink type	Python
276	O	977. Squares of a Sorted Array	[H]array-two-pointers-opposite-direction	use shrink type	Python Java
277	O	11. Container With Most Water	[H]array-two-pointers-opposite-direction	use shrink type	Python Java
278	O	42. Trapping Rain Water	[H]array-two-pointers-opposite-direction	use shrink type	Python
279		948. Bag of Tokens	[H]array-two-pointers-opposite-direction	use shrink type	Python
280	O	125. Valid Palindrome	[H]array-two-pointers-opposite-direction	use shrink type	Python Java
281		680. Valid Palindrome II	[H]array-two-pointers-opposite-direction	use shrink type	Python
282		344. Reverse String	[H]array-two-pointers-opposite-direction	use shrink type	Python Java
283		151. Reverse Words in a String	[H]array-two-pointers-opposite-direction	use shrink type	Python
284	O	5. Longest Palindromic Substring	[H]array-two-pointers-opposite-direction	use expand type	Python Java
285	O	179. Largest Number	[H]array-sort	use self defined sort	Python
286	O	215. Kth Largest Element in an Array	[H]array-sort	top k problem (based on sort)	Python Java
287		347. Top K Frequent Elements	[H]array-sort	top k problem (based on sort)	Python Java
288		1985. Find the Kth Largest Integer in the Array	[H]array-sort	top k problem (based on sort)	Python
289		1710. Maximum Units on a Truck	[H]array-sort	use bucket sort	Python
290		451. Sort Characters By Frequency	[H]array-sort	use bucket sort	Python
291		1099. Two Sum Less Than K	[H]array-sort	use bucket sort	Python
292		164. Maximum Gap	[H]array-sort	use bucket sort	Python
293		462. Minimum Moves to Equal Array Elements II	[H]array-sort	use quick select	Python
294		324. Wiggle Sort II	[H]array-sort	use quick select	Python
295		315. Count of Smaller Numbers After Self	[H]array-sort	use merge sort	Python
296		493. Reverse Pairs	[H]array-sort	use merge sort	Python
297		`stack-queue note`	[I]stack-queue
298		346. Moving Average from Data Stream	[I]stack-queue	use queue to simulate	Python
299	O	20. Valid Parentheses	[I]stack-queue	use stack to store the last states	Python Java
300	O	150. Evaluate Reverse Polish Notation	[I]stack-queue	use stack to store the last states	Python Java
301	O	224. Basic Calculator	[I]stack-queue	use stack to store the last states	Python
302	O	227. Basic Calculator II	[I]stack-queue	use stack to store the last states	Python
303		772. Basic Calculator III	[I]stack-queue	use stack to store the last states	Python
304	O	735. Asteroid Collision	[I]stack-queue	use stack to store the last states	Python
305	O	394. Decode String	[I]stack-queue	use stack to store the last states	Python
306		1209. Remove All Adjacent Duplicates in String II	[I]stack-queue	use stack to store the last states	Python
307		726. Number of Atoms	[I]stack-queue	use stack to store the last states	Python
308		71. Simplify Path	[I]stack-queue	use stack to store the last states	Python
309	O	232. Implement Queue using Stacks	[I]stack-queue	implement stack/queue	Python Java
310		225. Implement Stack using Queues	[I]stack-queue	implement stack/queue	Python
311	O	155. Min Stack	[I]stack-queue	implement stack/queue	Python Java
312		716. Max Stack	[I]stack-queue	implement stack/queue	Python
313	O	895. Maximum Frequency Stack	[I]stack-queue	implement stack/queue	Python
314	O	32. Longest Valid Parentheses	[I]stack-queue	use variables to simulate stack	Python
315		1249. Minimum Remove to Make Valid Parentheses	[I]stack-queue	use variables to simulate stack	Python
316		2296. Design a Text Editor	[I]stack-queue	use stack to simulate	Python
317		341. Flatten Nested List Iterator	[I]stack-queue	use stack to simulate	Python
318	O	239. Sliding Window Maximum	[I]stack-queue-monotonic	use monotonic queue and sliding window	Python
319		1438. Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit	[I]stack-queue-monotonic	use monotonic queue and sliding window	Python
320		1696. Jump Game VI	[I]stack-queue-monotonic	use monotonic queue and sliding window	Python
321		862. Shortest Subarray with Sum at Least K	[I]stack-queue-monotonic	use monotonic queue and sliding window	Python
322	O	739. Daily Temperatures	[I]stack-queue-monotonic	use monotonic stack (consider one side’s relationship)	Python Java
323		496. Next Greater Element I	[I]stack-queue-monotonic	use monotonic stack (consider one side’s relationship)	Python
324		503. Next Greater Element II	[I]stack-queue-monotonic	use monotonic stack (consider one side’s relationship)	Python
325		402. Remove K Digits	[I]stack-queue-monotonic	use monotonic stack (consider one side’s relationship)	Python
326		316. Remove Duplicate Letters	[I]stack-queue-monotonic	use monotonic stack (consider one side’s relationship)	Python
327		1762. Buildings With an Ocean View	[I]stack-queue-monotonic	use monotonic stack (consider one side’s relationship)	Python
328		1944. Number of Visible People in a Queue	[I]stack-queue-monotonic	use monotonic stack (consider one side’s relationship)	Python
329		2345. Finding the Number of Visible Mountains	[I]stack-queue-monotonic	use monotonic stack (consider one side’s relationship)	Python
330		768. Max Chunks To Make Sorted II	[I]stack-queue-monotonic	use monotonic stack (consider one side’s relationship)	Python
331		2289. Steps to Make Array Non-decreasing	[I]stack-queue-monotonic	use monotonic stack (consider one side’s relationship)	Python
332	O	84. Largest Rectangle in Histogram	[I]stack-queue-monotonic	use monotonic stack (consider two side’s relationship)	Python
333		85. Maximal Rectangle	[I]stack-queue-monotonic	use monotonic stack (consider two side’s relationship)	Python
334		907. Sum of Subarray Minimums	[I]stack-queue-monotonic	use monotonic stack (consider two side’s relationship)	Python
335		2104. Sum of Subarray Ranges	[I]stack-queue-monotonic	use monotonic stack (consider two side’s relationship)	Python
336		1856. Maximum Subarray Min-Product	[I]stack-queue-monotonic	use monotonic stack (consider two side’s relationship)	Python
337		`backtracking note`	[J]backtracking
338	O	78. Subsets	[J]backtracking	subset	Python Java
339	O	39. Combination Sum	[J]backtracking	subset	Python Java
340		90. Subsets II	[J]backtracking	subset	Python
341		40. Combination Sum II	[J]backtracking	subset	Python
342	O	46. Permutations	[J]backtracking	permutation	Python Java
343		47. Permutations II	[J]backtracking	permutation	Python
344		267. Palindrome Permutation II	[J]backtracking	permutation	Python
345		77. Combinations	[J]backtracking	combination	Python
346		216. Combination Sum III	[J]backtracking	combination	Python
347	O	17. Letter Combinations of a Phone Number	[J]backtracking	backtracking with constraints	Python Java
348	O	22. Generate Parentheses	[J]backtracking	backtracking with constraints	Python
349	O	113. Path Sum II	[J]backtracking	backtracking with constraints	Python
350	O	437. Path Sum III	[J]backtracking	backtracking with constraints	Python
351	O	79. Word Search	[J]backtracking	backtracking with constraints	Python Java
352	O	212. Word Search II	[J]backtracking	backtracking with constraints	Python
353	O	37. Sudoku Solver	[J]backtracking	backtracking with constraints	Python
354	O	51. N-Queens	[J]backtracking	backtracking with constraints	Python
355		465. Optimal Account Balancing	[J]backtracking	backtracking with constraints	Python
356		93. Restore IP Addresses	[J]backtracking	backtracking with constraints	Python
357		140. Word Break II	[J]backtracking	backtracking with constraints	Python
358		257. Binary Tree Paths	[J]backtracking	backtracking with constraints	Python
359		131. Palindrome Partitioning	[J]backtracking	backtracking with constraints	Python
360		`graph note`	[K]graph
361	O	329. Longest Increasing Path in a Matrix	[K]graph-dfs	dfs	Python
362		1059. All Paths from Source Lead to Destination	[K]graph-dfs	dfs	Python
363	O	200. Number of Islands	[K]graph-bfs	bfs with single source	Python Java
364	O	733. Flood Fill	[K]graph-bfs	bfs with single source	Python Java
365	O	1730. Shortest Path to Get Food	[K]graph-bfs	bfs with single source	Python
366	O	1197. Minimum Knight Moves	[K]graph-bfs	bfs with single source	Python
367	O	261. Graph Valid Tree	[K]graph-bfs	bfs with single source	Python
368	O	127. Word Ladder	[K]graph-bfs	bfs with single source	Python
369	O	133. Clone Graph	[K]graph-bfs	bfs with single source	Python Java
370	O	815. Bus Routes	[K]graph-bfs	bfs with single source	Python
371		695. Max Area of Island	[K]graph-bfs	bfs with single source	Python
372		1905. Count Sub Islands	[K]graph-bfs	bfs with single source	Python
373		1345. Jump Game IV	[K]graph-bfs	bfs with single source	Python
374		1091. Shortest Path in Binary Matrix	[K]graph-bfs	bfs with single source	Python
375		1992. Find All Groups of Farmland	[K]graph-bfs	bfs with single source	Python
376		909. Snakes and Ladders	[K]graph-bfs	bfs with single source	Python
377		749. Contain Virus	[K]graph-bfs	bfs with single source	Python
378		694. Number of Distinct Islands	[K]graph-bfs	bfs with single source	Python
379	O	542. 01 Matrix	[K]graph-bfs	bfs with multiple sources	Python Java
380	O	417. Pacific Atlantic Water Flow	[K]graph-bfs	bfs with multiple sources	Python
381	O	994. Rotting Oranges	[K]graph-bfs	bfs with multiple sources	Python Java
382		286. Walls and Gates	[K]graph-bfs	bfs with multiple sources	Python
383		130. Surrounded Regions	[K]graph-bfs	bfs with multiple sources	Python
384		126. Word Ladder II	[K]graph-bfs	bfs with hashset as queue	Python
385		301. Remove Invalid Parentheses	[K]graph-bfs	bfs with hashset as queue	Python
386	O	721. Accounts Merge	[K]graph-union-find	union find	Python Java
387	O	323. Number of Connected Components in an Undirected Graph	[K]graph-union-find	union find	Python
388		547. Number of Provinces	[K]graph-union-find	union find	Python
389		2316. Count Unreachable Pairs of Nodes in an Undirected Graph	[K]graph-union-find	union find	Python
390		399. Evaluate Division	[K]graph-union-find	union find	Python
391		305. Number of Islands II	[K]graph-union-find	union find	Python
392		1101. The Earliest Moment When Everyone Become Friends	[K]graph-union-find	union find	Python
393		2421. Number of Good Paths	[K]graph-union-find	union find	Python
394		1102. Path With Maximum Minimum Value	[K]graph-union-find	union find	Python
395		737. Sentence Similarity II	[K]graph-union-find	union find	Python
396	O	207. Course Schedule	[K]graph-kahn	kahn (topological sort)	Python Java
397	O	210. Course Schedule II	[K]graph-kahn	kahn (topological sort)	Python
398	O	269. Alien Dictionary	[K]graph-kahn	kahn (topological sort)	Python
399	O	310. Minimum Height Trees	[K]graph-kahn	kahn (topological sort)	Python Java
400		2115. Find All Possible Recipes from Given Supplies	[K]graph-kahn	kahn (topological sort)	Python
401		802. Find Eventual Safe States	[K]graph-kahn	kahn (topological sort)	Python
402		1136. Parallel Courses	[K]graph-kahn	kahn (topological sort)	Python
403		2050. Parallel Courses III	[K]graph-kahn	kahn (topological sort)	Python
404		1203. Sort Items by Groups Respecting Dependencies	[K]graph-kahn	kahn (topological sort)	Python
405		2192. All Ancestors of a Node in a Directed Acyclic Graph	[K]graph-kahn	kahn (topological sort)	Python
406		743. Network Delay Time	[K]graph-dijkstra	dijkstra (shortest path)	Python
407		778. Swim in Rising Water	[K]graph-dijkstra	dijkstra (shortest path)	Python
408		1514. Path with Maximum Probability	[K]graph-dijkstra	dijkstra (shortest path)	Python
409		505. The Maze II	[K]graph-dijkstra	dijkstra (shortest path)	Python
410		2093. Minimum Cost to Reach City With Discounts	[K]graph-dijkstra	dijkstra (shortest path)	Python
411	O	787. Cheapest Flights Within K Stops	[K]graph-bellman-ford	bellman ford (shortest path)	Python
412		1334. Find the City With the Smallest Number of Neighbors at a Threshold Distance	[K]graph-floyd-warshall	floyd warshall (shortest path)	Python
413		1135. Connecting Cities With Minimum Cost	[K]graph-kruskal	kruskal (mst)	Python
414		1584. Min Cost to Connect All Points	[K]graph-kruskal	kruskal (mst)	Python
415		1168. Optimize Water Distribution in a Village	[K]graph-kruskal	kruskal (mst)	Python
416		1489. Find Critical and Pseudo-Critical Edges in Minimum Spanning Tree	[K]graph-kruskal	kruskal (mst)	Python
417		1724. Checking Existence of Edge Length Limited Paths II	[K]graph-kruskal	kruskal (mst)	Python
418		1192. Critical Connections in a Network	[K]graph-tarjan	tarjan (scc)	Python
419		332. Reconstruct Itinerary	[K]graph-hierholzer	hierholzer (eulerian path)	Python
420		753. Cracking the Safe	[K]graph-hierholzer	hierholzer (eulerian path)	Python
421	O	54. Spiral Matrix	[K]graph-matrix	matrix	Python Java
422	O	48. Rotate Image	[K]graph-matrix	matrix	Python
423	O	73. Set Matrix Zeroes	[K]graph-matrix	matrix	Python
424		1582. Special Positions in a Binary Matrix	[K]graph-matrix	matrix	Python
425		348. Design Tic-Tac-Toe	[K]graph-matrix	matrix	Python
426		`bit-manipulation note`	[L]bit-manipulation
427	O	136. Single Number	[L]bit-manipulation	xor	Python Java
428	O	268. Missing Number	[L]bit-manipulation	xor	Python Java
429	O	191. Number of 1 Bits	[L]bit-manipulation	shift	Python Java
430	O	190. Reverse Bits	[L]bit-manipulation	shift	Python Java
431		1356. Sort Integers by The Number of 1 Bits	[L]bit-manipulation	shift	Python
432	O	36. Valid Sudoku	[L]bit-manipulation	bitmasking	Python
433		1915. Number of Wonderful Substrings	[L]bit-manipulation	bitmasking	Python
434		1542. Find Longest Awesome Substring	[L]bit-manipulation	bitmasking	Python
435		`dynamic-programming note`	[M]dynamic-programming
436	O	62. Unique Paths	[M]dynamic-programming	2D	Python Java
437		63. Unique Paths II	[M]dynamic-programming	2D	Python
438	O	221. Maximal Square	[M]dynamic-programming	2D	Python
439		64. Minimum Path Sum	[M]dynamic-programming	2D	Python
440		688. Knight Probability in Chessboard	[M]dynamic-programming	2D	Python
441	O	416. Partition Equal Subset Sum	[M]dynamic-programming	knapsack (0-1 knapsack)	Python Java
442		494. Target Sum	[M]dynamic-programming	knapsack (0-1 knapsack)	Python
443		1049. Last Stone Weight II	[M]dynamic-programming	knapsack (0-1 knapsack)	Python
444		474. Ones and Zeroes	[M]dynamic-programming	knapsack (0-1 knapsack)	Python
445	O	322. Coin Change	[M]dynamic-programming	knapsack (complete knapsack)	Python Java
446		279. Perfect Squares	[M]dynamic-programming	knapsack (complete knapsack)	Python
447		518. Coin Change II	[M]dynamic-programming	knapsack (combination knapsack)	Python
448	O	377. Combination Sum IV	[M]dynamic-programming	knapsack (permutation knapsack)	Python
449	O	70. Climbing Stairs	[M]dynamic-programming	linear sequence	Python Java
450	O	55. Jump Game	[M]dynamic-programming	linear sequence	Python
451	O	198. House Robber	[M]dynamic-programming	linear sequence	Python Java
452		213. House Robber II	[M]dynamic-programming	linear sequence	Python
453	O	152. Maximum Product Subarray	[M]dynamic-programming	linear sequence	Python
454	O	91. Decode Ways	[M]dynamic-programming	linear sequence	Python
455	O	139. Word Break	[M]dynamic-programming	linear sequence	Python Java
456		256. Paint House	[M]dynamic-programming	linear sequence	Python
457		123. Best Time to Buy and Sell Stock III	[M]dynamic-programming	linear sequence	Python
458		309. Best Time to Buy and Sell Stock with Cooldown	[M]dynamic-programming	linear sequence	Python
459		376. Wiggle Subsequence	[M]dynamic-programming	linear sequence	Python
460		487. Max Consecutive Ones II	[M]dynamic-programming	linear sequence	Python
461		368. Largest Divisible Subset	[M]dynamic-programming	linear sequence	Python
462		1105. Filling Bookcase Shelves	[M]dynamic-programming	linear sequence	Python
463	O	300. Longest Increasing Subsequence	[M]dynamic-programming	LIS	Python
464		1964. Find the Longest Valid Obstacle Course at Each Position	[M]dynamic-programming	LIS	Python
465		354. Russian Doll Envelopes	[M]dynamic-programming	LIS	Python
466		1143. Longest Common Subsequence	[M]dynamic-programming	double sequence	Python
467		72. Edit Distance	[M]dynamic-programming	double sequence	Python
468		97. Interleaving String	[M]dynamic-programming	double sequence	Python
469		115. Distinct Subsequences	[M]dynamic-programming	double sequence	Python
470		1092. Shortest Common Supersequence	[M]dynamic-programming	double sequence	Python
471		10. Regular Expression Matching	[M]dynamic-programming	double sequence	Python
472		410. Split Array Largest Sum	[M]dynamic-programming	interval (start from one interval)	Python
473		1335. Minimum Difficulty of a Job Schedule	[M]dynamic-programming	interval (start from one interval)	Python
474		1278. Palindrome Partitioning III	[M]dynamic-programming	interval (start from one interval)	Python
475		312. Burst Balloons	[M]dynamic-programming	interval (start from short interval)	Python
476		516. Longest Palindromic Subsequence	[M]dynamic-programming	interval (start from short interval)	Python
477		647. Palindromic Substrings	[M]dynamic-programming	interval (start from short interval)	Python
478		1547. Minimum Cost to Cut a Stick	[M]dynamic-programming	interval (start from short interval)	Python
479		`greedy note`	[N]greedy
480	O	53. Maximum Subarray	[N]greedy	greedy	Python Java
481	O	134. Gas Station	[N]greedy	greedy	Python Java
482	O	621. Task Scheduler	[N]greedy	greedy	Python Java
483		45. Jump Game II	[N]greedy	greedy	Python
484		665. Non-decreasing Array	[N]greedy	greedy	Python
485		135. Candy	[N]greedy	greedy	Python
486		277. Find the Celebrity	[N]greedy	greedy	Python
487		406. Queue Reconstruction by Height	[N]greedy	greedy	Python
488		659. Split Array into Consecutive Subsequences	[N]greedy	greedy	Python
489		763. Partition Labels	[N]greedy	greedy	Python
490		926. Flip String to Monotone Increasing	[N]greedy	greedy	Python
491		1567. Maximum Length of Subarray With Positive Product	[N]greedy	greedy	Python
492		1864. Minimum Number of Swaps to Make the Binary String Alternating	[N]greedy	greedy	Python
493		2366. Minimum Replacements to Sort the Array	[N]greedy	greedy	Python
494		2870. Minimum Number of Operations to Make Array Empty	[N]greedy	greedy	Python
495		`math note`	[O]math
496		204. Count Primes	[O]math	sieve of eratosthenes	Python
497	O	50. Pow(x, n)	[O]math	exponentiation by squaring	Python
498		470. Implement Rand10() Using Rand7()	[O]math	rejection sampling	Python
499	O	7. Reverse Integer	[O]math	math	Python
500	O	9. Palindrome Number	[O]math	math	Python Java
501	O	67. Add Binary	[O]math	math	Python Java
502	O	338. Counting Bits	[O]math	math	Python Java
503		415. Add Strings	[O]math	math	Python
504		263. Ugly Number	[O]math	math	Python
505		258. Add Digits	[O]math	math	Python
506		171. Excel Sheet Column Number	[O]math	math	Python
507		869. Reordered Power of 2	[O]math	math	Python
508		391. Perfect Rectangle	[O]math	math	Python
509		`segment-tree note`	[P]segment-tree
510		307. Range Sum Query - Mutable	[P]segment-tree	use sum type segment tree	Python
511		715. Range Module	[P]segment-tree	use count type segment tree	Python
512		729. My Calendar I	[P]segment-tree	use count type segment tree	Python
513		2158. Amount of New Area Painted Each Day	[P]segment-tree	use count type segment tree	Python
514		218. The Skyline Problem	[P]segment-tree	use max type segment tree	Python
515		2407. Longest Increasing Subsequence II	[P]segment-tree	use max type segment tree	Python
516		731. My Calendar II	[P]segment-tree	use max type segment tree	Python
517		`basic note`	[Q]basic

How to crack LeetCode problems?

For beginners tackling 0-50 problems, I suggest starting with curated lists like the Blind 75, Grind 75, or NeetCode 150. It's crucial to begin with EASY problems. If you stumble upon unfamiliar concepts, don't hesitate to seek explanations from sources like ChatGPT or the LeetCode discussion section. Aim to accomplish three key objectives during this phase: familiarize yourself with the syntax of common data structures like hashmaps or stacks, gain a holistic understanding of necessary DSA topics, and grasp at least the brute force solution approach, along with basic analyses of time and space complexity for each problem.
For intermediates solving 50-150 problems, understanding how and why to evolve from brute force to more efficient or optimal solutions is vital. Grasping this transition process is crucial, not just memorizing solutions. At this stage, deeply comprehending the improvement mechanism is the key focus. Often, the breakpoint for a better solution comes from identifying and refining repetitive elements in the old approach.
After solving over 150 problems, you'll likely have covered around 85% of the topics that could appear in coding interviews. The key at this phase is to recognize patterns across the multitude of problems available. Most questions are variations of a few core concepts or classic problems you've already encountered. Identifying these patterns allows you to apply known solutions to new, seemingly complex problems effectively. Additionally, you should start using different approaches to solve the same problem you already know. For example, if it is a DFS problem, then try both recursive and iterative methods; if it is a DP problem, try both top-down and bottom-up approaches; if it is a top-k problem, then try using a heap or sort. Furthermore, attempt to understand other solutions that use approaches that are not as straightforward as your old solutions. At this stage, it's crucial to recognize recurring patterns across various problems, understanding both the application of consistent approaches to different questions and the exploration of multiple strategies for a single problem. This dual awareness enables a more adaptable and comprehensive problem-solving skill set.

How to prepare for a coding interview?

During the interview, consistently share your thoughts with the interviewer and use code comments to note down things while speaking. This ensures both of you are aligned.

Clarify the requirement of the question. You must truly understand what the question is asking for. Once you understand the question’s description, make sure to generate a simple input and expect output other than the given one based on your understanding and ask the interviewer if it is correct or not.
Clarify the input and output and edge cases. For instance, ask if the input array is sorted or not, whether numbers can include positives, negatives, or zeros, or if the input contains duplicate elements or not, and how to handle multiple valid answers, whether to return the first one or if outputs need sorting, and what is the expected outcome when there are no valid solutions. Take LC 209. Minimum Size Subarray Sum as example, if numbers in the input array can be negative, the question will become LC 862. Shortest Subarray with Sum at Least K, and will need a totally different approach to solve.
Start from a brute force approach, just write some very simple pseudo steps of it. If you have ideas to improve it, then you can continue to explain how and where you can improve and use which DSA or classic pattern (like prefix sum, trie, or two pointers) to solve it. Mention the expected time and space complexity. If you do not have any clue to improve the naive approach, then just ask the interviewer, can we start from implementing this naive approach or not, sometimes you would find out the key point during implementing. If it is not allowed, then try to analyze some common DSA which might be useful here to the interviewer and try to get some feedback or hints from the interviewer. (If brute force is still too hard to get, then try to simulate the whole process in the description of the question or try to enumerate things).
Implement the solution, adhering to proper coding style and indentation. If stuck on certain code, ask to finish the main logic first and leave comments for unimplemented parts. If stuck on the main logic, share your thoughts and discuss potential next steps with the interviewer.
Final check and dry run. Once finished, do not directly run the code, because there might be some stupid typos in the code. Ask if you can dry run one time, and explain the whole process and your thoughts.
Test and debug. Generate 1 or 2 standard cases and 1 or 2 edge cases which are related to the problem. And start testing and debugging. Avoid trial and error multiple times when debugging. Fix the error you find, and try to quickly dry run once and explain why you fix the error.
Complexity analysis. Try to analyze the time and space complexity about your solutions and try to mention some potential follow up questions you have thought of. Like what if we change the condition of the input, or what if we have a limitation on time or space usage.

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LeetCode Pattern 500 offers 500 solutions for LeetCode problems in Python and Java, 17 notes on essential concepts related to data structures and algorithms, and 130 patterns for solving LeetCode problems.

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