LeetCode

Algorithm and data structure solutions in Java 8 / JavaScript.

*: LintCode | **: HackerRank | ***: GeeksforGeeks

Topics

• Array
• String
• Binary Tree
• Binary Search
• Linked List
• HashMap
• Queue
• Heap
• Two Pointers
• Math
• Bit Manipulation
• Breadth-First Search
• Depth-First Search
• Backtracking
• Stack
• Dynamic Programming
• Sort
• Greedy
• Graph
• Trie
• Union Find
• Design

OJ (LeetCode & LintCode)

Title	Solution	Difficulty
001. Two Sum	Solution	Easy
002. Add Two Numbers	Solution	Medium
003. Longest Substring Without Repeating Characters	Solution	Medium
004. Median of Two Sorted Arrays	Solution	Hard
005. Longest Palindromic Substring	Solution	Medium
006. ZigZag Conversion	Solution	Medium
007. Reverse Integer	Solution	Easy
008. String to Integer (atoi)	Solution	Medium
009. Palindrome Number	Solution	Easy
010. Regular Expression Matching	Solution	Hard
012. Integer to Roman	Solution	Medium
013. Roman to Integer	Solution	Easy
014. Longest Common Prefix	Solution	Easy
015. 3Sum	Solution	Medium
016. 3Sum Closest	Solution	Medium
017. Letter Combinations of a Phone Number	Solution	Medium
019. Remove Nth Node From End of List	Solution	Medium
021. Merge Two Sorted Lists	Solution	Easy
022. Generate Parentheses	Solution	Medium
023. Merge k Sorted Lists	Solution	Hard
024. Swap Nodes in Pairs	Solution	Medium
026. Remove Duplicates from Sorted Array	Solution	Easy
028. Implement_strStr()	Solution	Easy
029. Divide Two Integers	Solution	Medium
031. Next Permutation	Solution	Medium
032. Longest Valid Parentheses	Solution	Hard
033. Search in Rotated Sorted Array	Solution	Medium
034. Find First and Last Position of Element in Sorted Array	Solution	Medium
035. Search Insert Position	Solution	Easy
036. Valid Sudoku	Solution	Medium
039. Combination Sum	Solution	Medium
041. First Missing Positive	Solution	Hard
042. Trapping Rain Water	Solution	Hard
043. Multiply Strings	Solution	Medium
045. Jump Game II	Solution	Hard
046. Permutations	Solution	Medium
047. Permutations II	Solution	Medium
048. Rotate Image	Solution	Medium
049. Group Anagrams	Solution	Medium
050. Pow(x, n)	Solution	Medium
053. Maximum Subarray	Solution	Easy
054. Spiral Matrix	Solution	Medium
055. Jump Game	Solution	Medium
056. Merge Intervals	Solution	Medium
059. Spiral Matrix II	Solution	Medium
061. Rotate List	Solution	Medium
062. Unique Paths	Solution	Medium
063. Unique Paths II	Solution	Medium
064. Minimum Path Sum	Solution	Medium
066. Plus One	Solution	Easy
067. Add Binary	Solution	Easy
068. Text Justification	Solution	Hard
069. Sqrt(x)	Solution	Easy
070. Climbing Stairs	Solution	Easy
072. Edit Distance	Solution	Hard
073. Set Matrix Zeroes	Solution	Medium
074. Search a 2D Matrix	Solution	Medium
075. Sort Colors	Solution	Medium
076. Minimum Window Substring	Solution	Hard
078. Subsets	Solution	Medium
083. Remove Duplicates from Sorted List	Solution	Easy
088. Merge Sorted Array	Solution	Easy
094. Binary Tree Inorder Traversal	Solution	Medium
091. Decode Ways	Solution	Medium
098. Validate Binary Search Tree	Solution	Medium
101. Symmetric Tree	Solution	Easy
102. Binary Tree Level Order Traversal	Solution	Medium
103. Binary Tree Zigzag Level Order Traversal	Solution	Medium
104. Maximum Depth of Binary Tree	Solution	Easy
105. Construct Binary Tree from Preorder and Inorder Traversal	Solution	Medium
108. Convert Sorted Array to Binary Search Tree	Solution	Easy
112. Path Sum	Solution	Easy
113. Path Sum II	Solution	Medium
114. Flatten Binary Tree to Linked List	Solution	Medium
116. Populating Next Right Pointers in Each Node	Solution	Medium
119. Pascal's Triangle II	Solution	Easy
120. Triangle	Solution	Medium
121. Best Time to Buy and Sell Stock	Solution	Easy
122. Best Time to Buy and Sell Stock II	Solution	Easy
124. Binary Tree Maximum Path Sum	Solution	Hard
126. Word Ladder II	Solution	Hard
127. Word Ladder	Solution	Medium
128. Longest Consecutive Sequence	Solution	Hard
130. Surrounded Regions	Solution	Medium
131. Palindrome Partitioning	Solution	Medium
133. Clone Graph	Solution	Medium
134. Gas Station	Solution	Medium
136. Single Number	Solution	Easy
139. Word Break	Solution	Medium
140. Word Break II	Solution	Hard
141. Linked List Cycle	Solution	Easy
144. Binary Tree Preorder Traversal	Solution	Medium
146. LRU Cache	Solution	Hard
148. Sort List	Solution	Medium
150. Evaluate Reverse Polish Notation	Solution	Medium
151. Reverse Words in a String	Solution	Medium
152. Maximum Product Subarray	Solution	Medium
155. Min Stack	Solution	Easy
159. Longest Substring with At Most Two Distinct Characters	Solution	Hard
160. Intersection of Two Linked Lists	Solution	Easy
162. Find Peak Element	Solution	Medium
163. Missing Ranges	Solution	Medium
167. Two Sum II - Input array is sorted	Solution	Easy
166. Fraction to Recurring Decimal	Solution	Medium
168. Excel Sheet Column Title	Solution	Easy
173. Binary Search Tree Iterator	Solution	Medium
179. Largest Number	Solution	Medium
189. Rotate Array	Solution	Easy
198. House Robber	Solution	Easy
199. Binary Tree Right Side View	Solution	Medium
200. Number of Islands	Solution	Medium
205. Isomorphic Strings	Solution	Easy
206. Reverse Linked List	Java/JS	Easy
207. Course Schedule	Java	Medium
208. Implement Trie (Prefix Tree)	Java	Medium
209. Minimum Size Subarray Sum	Solution	Medium
210. Course Schedule II	Solution	Medium
211. Add and Search Word - Data structure design	Solution	Medium
212. Word Search II	Solution	Hard
213. House Robber II	Solution	Medium
215. Kth Largest Element in an Array	Solution	Medium
218. The Skyline Problem	Solution	Hard
221. Maximal Square	Solution	Medium
224. Basic Calculator	Solution	Hard
227. Basic Calculator II	Java/JS	Medium
228. Summary Ranges	Solution	Medium
231. Power of Two	Solution	Easy
234. Palindrome Linked List	Solution	Easy
235. Lowest Common Ancestor of a Binary Search Tree	Solution	Easy
236. Lowest Common Ancestor of a Binary Tree	Solution	Medium
238. Product of Array Except Self	Solution	Medium
239. Sliding Window Maximum	Solution	Hard
240. Search a 2D Matrix II	Solution	Medium
242. Valid Anagram	Solution	Easy
243. Shortest Word Distance	Solution	Easy
244. Shortest Word Distance II	Solution	Medium
249. Group Shifted Strings	Solution	Medium
251. Flatten 2D Vector	Solution	Medium
252. Meeting Rooms	Solution	Easy
253. Meeting Rooms II	Solution	Medium
257. Binary Tree Paths	Solution	Easy
258. Add Digits	Solution	Easy
261. Graph Valid Tree	Solution	Medium
266. Palindrome Permutation	Solution	Easy
269. Alien Dictionary	Solution	Hard
268. Missing Number	Solution	Easy
277. Find the Celebrity	Java/JS	Medium
273. Integer to English Words	Solution	Hard
279. Perfect Squares	Solution	Medium
280. Wiggle Sort	Solution	Medium
289. Game of Life	Solution	Medium
295. Find Median from Data Stream	Solution	Hard
297. Serialize and Deserialize Binary Tree	Solution	Hard
300. Longest Increasing Subsequence	Solution	Medium
305. Number of Islands II	Solution	Hard
312. Burst Balloons	Solution	Hard
316. Remove Duplicate Letters	Solution	Hard
324. Wiggle Sort II	Solution	Hard
326. Power of Three	Solution	Easy
329. Longest Increasing Path in a Matrix	Solution	Hard
336. Palindrome Pairs	Solution	Hard
340. Longest Substring with At Most K Distinct Characters	Solution	Hard
341. Flatten Nested List Iterator	Solution	Medium
342. Power of Four	Solution	Easy
344. Reverse String	Java/JS	Easy
345. Reverse Vowels of a String	Solution	Easy
347. Top K Frequent Elements	Solution	Medium
359. Logger Rate Limiter	Solution	Easy
367. Valid Perfect Square	Solution	Easy
369. Plus One Linked List	Solution	Medium
373. Find K Pairs with Smallest Sums	Solution	Medium
378. Kth Smallest Element in a Sorted Matrix	Solution	Medium
380. Insert Delete GetRandom O(1)	Solution	Medium
387. First Unique Character in a String	Solution	Easy
406. Queue Reconstruction by Height	Solution	Medium
418. Sentence Screen Fitting	Solution	Medium
421. Maximum XOR of Two Numbers in an Array)	Solution	Medium
425. Word Squares	Solution	Hard
441. Arranging Coins	Solution	Easy
442. Find All Duplicates in an Array	Solution	Medium
443. String Compression	Solution	Medium
448. Find All Numbers Disappeared in an Array	Solution	Easy
463. Island Perimeter	Solution	Easy
482. License Key Formatting	Solution	Easy
490. The Maze	Solution	Medium
507. Perfect Number	Solution	Easy
557. Reverse Words in a String III	Solution	Easy
564. Find the Closest Palindrome	Solution	Hard
582. Kill Process	Solution	Medium
617. Merge Two Binary Trees	Solution	Easy
632. Smallest Range	Solution	Hard
633. Sum of Square Numbers	Solution	Easy
642. Design Search Autocomplete System	Solution	Hard
647. Palindromic Substrings	Solution	Medium
657. Judge Route Circle	Solution	Easy
657. Robot Return to Origin	Solution	Easy
674. Longest Continuous Increasing Subsequence	Solution	Easy
681. Next Closest Time	Solution	Medium
684. Redundant Connection	Solution	Medium
688. Knight Probability in Chessboard	Solution	Medium
692. Top K Frequent Words	Solution	Medium
695. Max Area of Island	Solution	Easy
703. Kth Largest Element in a Stream	Solution	Easy
721. Accounts Merge	Solution	Medium
737. Sentence Similarity II	Solution	Medium
739. Daily Temperatures	Solution	Medium
746. Min Cost Climbing Stairs	Solution	Easy
751. IP to CIDR	Solution	Easy
755. Pour Water	Solution	Medium
756. Pyramid Transition Matrix	Solution	Medium
759. Employee Free Time	Solution	Hard
760. Find Anagram Mappings	Solution	Easy
763. Partition Labels	Solution	Medium
765. Couples Holding Hands	Solution	Hard
771. Jewels and Stones	Solution	Easy
772. Basic Calculator III	Solution	Hard
773. Sliding Puzzle	Solution	Hard
781. Rabbits in Forest	Solution	Medium
787. Cheapest Flights Within K Stops	Solution	Medium
807. Max Increase to Keep City Skyline	Solution	Medium
811. Subdomain Visit Count	Solution	Easy
815. Bus Routes	Solution	Hard
829. Consecutive Numbers Sum	Solution	Hard
832. Flipping an Image	Solution	Easy
843. Guess the Word	Solution	Hard
904. Fruit Into Baskets	Solution	Medium
*109. Triangle	Solution	Easy
*382. Triangle Count	Solution	Medium
*464. Sort Integers II	Solution	Easy
*589. Connecting Graph	Solution	Medium
*590. Connecting Graph II	Solution	Medium
*591. Connecting Graph III	Solution	Medium
*609. Two Sum - Less than or equal to target	Solution	Medium
**Count Duplicates	Solution	Easy
**Implement Stack By LinkedList	Solution	Easy
**Delete Node Greater than X	Solution	Easy
**Merge in Between.java	Solution	Easy
**Expression_Token	Solution	Easy
**Build Subsequences	Solution	Easy
**Merge in Between	Solution	Medium
**Missing Words	Solution	Easy
**Shift Letters	Solution	Easy
**Friends Graph	Solution	Easy
***Check_Binary_String.java	Solution	Easy
***Remove_Duplicates_from_Unsorted_Array.java	Solution	Easy

Array

Title	Solution	Difficulty
001. Two Sum	Solution	Easy
015. 3Sum	Solution	Medium
016. 3Sum Closest	Solution	Medium
026. Remove Duplicates from Sorted Array	Solution	Easy
031. Next Permutation	Solution	Medium
033. Search in Rotated Sorted Array	Solution	Medium
034. Find First and Last Position of Element in Sorted Array	Solution	Medium
035. Search Insert Position	Solution	Easy
039. Combination Sum	Solution	Medium
041. First Missing Positive	Solution	Hard
042. Trapping Rain Water	Solution	Hard
045. Jump Game II	Solution	Hard
046. Permutations	Solution	Medium
047. Permutations II	Solution	Medium
048. Rotate Image	Solution	Medium
053. Maximum Subarray	Solution	Easy
054. Spiral Matrix	Solution	Medium
056. Merge Intervals	Solution	Medium
059. Spiral Matrix II	Solution	Medium
062. Unique Paths	Solution	Medium
063. Unique Paths II	Solution	Medium
064. Minimum Path Sum	Solution	Medium
066. Plus One	Solution	Easy
073. Set Matrix Zeroes	Solution	Medium
075. Sort Colors	Solution	Medium
078. Subsets	Solution	Medium
088. Merge Sorted Array	Solution	Easy
091. Decode Ways	Solution	Medium
119. Pascal's Triangle II	Solution	Easy
120. Triangle	Solution	Medium
121. Best Time to Buy and Sell Stock	Solution	Easy
122. Best Time to Buy and Sell Stock II	Solution	Easy
128. Longest Consecutive Sequence	Solution	Hard
130. Surrounded Regions	Solution	Medium
134. Gas Station	Solution	Medium
136. Single Number	Solution	Easy
152. Maximum Product Subarray	Solution	Medium
163. Missing Ranges	Solution	Medium
167. Two Sum II - Input array is sorted	Solution	Easy
189. Rotate Array	Solution	Easy
198. House Robber	Solution	Easy
209. Minimum Size Subarray Sum	Solution	Medium
218. The Skyline Problem	Solution	Hard
277. Find the Celebrity	Java/JS	Medium
228. Summary Ranges	Solution	Medium
238. Product of Array Except Self	Solution	Medium
243. Shortest Word Distance	Solution	Easy
244. Shortest Word Distance II	Solution	Medium
253. Meeting Rooms II	Solution	Medium
280. Wiggle Sort	Solution	Medium
289. Game of Life	Solution	Medium
300. Longest Increasing Subsequence	Solution	Medium
380. Insert Delete GetRandom O(1)	Solution	Medium
442. Find All Duplicates in an Array	Solution	Medium
448. Find All Numbers Disappeared in an Array	Solution	Easy
463. Island Perimeter	Solution	Easy
674. Longest Continuous Increasing Subsequence	Solution	Easy
681. Next Closest Time	Solution	Medium
695. Max Area of Island	Solution	Easy
755. Pour Water	Solution	Medium
807. Max Increase to Keep City Skyline	Solution	Medium
832. Flipping an Image	Solution	Easy
*464. Sort Integers II	Solution	Easy
**Count Duplicates	Solution	Easy

String

Title	Solution	Difficulty
003. Longest Substring Without Repeating Characters	Solution	Medium
005. Longest Palindromic Substring	Solution	Medium
006. ZigZag Conversion	Solution	Medium
008. String to Integer (atoi)	Solution	Medium
010. Regular Expression Matching	Solution	Hard
012. Integer to Roman	Solution	Medium
013. Roman to Integer	Solution	Easy
014. Longest Common Prefix	Solution	Easy
017. Letter Combinations of a Phone Number	Solution	Medium
022. Generate Parentheses	Solution	Medium
049. Group Anagrams	Solution	Medium
028. Implement_strStr()	Solution	Easy
043. Multiply Strings	Solution	Medium
067. Add Binary	Solution	Easy
068. Text Justification	Solution	Hard
072. Edit Distance	Solution	Hard
076. Minimum Window Substring	Solution	Hard
126. Word Ladder II	Solution	Hard
127. Word Ladder	Solution	Medium
131. Palindrome Partitioning	Solution	Medium
150. Evaluate Reverse Polish Notation	Solution	Medium
151. Reverse Words in a String	Solution	Medium
162. Find Peak Element	Solution	Medium
227. Basic Calculator II	Solution	Medium
249. Group Shifted Strings	Solution	Medium
266. Palindrome Permutation	Solution	Easy
273. Integer to English Words	Solution	Hard
344. Reverse String	Solution	Easy
345. Reverse Vowels of a String	Solution	Easy
387. First Unique Character in a String	Solution	Easy
418. Sentence Screen Fitting	Solution	Medium
443. String Compression	Solution	Medium
482. License Key Formatting	Solution	Easy
772. Basic Calculator III	Solution	Hard
557. Reverse Words in a String III	Solution	Easy
564. Find the Closest Palindrome	Solution	Hard
647. Palindromic Substrings	Solution	Medium
657. Judge Route Circle	Solution	Easy
657. Robot Return to Origin	Solution	Easy
**Expression_Token	Solution	Easy
**Build Subsequences	Solution	Easy
**Merge in Between	Solution	Medium
**Missing Words	Solution	Easy
**Shift Letters	Solution	Easy
**Keyboard	Solution	Medium

Binary Tree

Title	Solution	Difficulty
094. Binary Tree Inorder Traversal	Solution	Medium
098. Validate Binary Search Tree	Solution	Medium
101. Symmetric Tree	Solution	Easy
102. Binary Tree Level Order Traversal	Solution	Medium
103. Binary Tree Zigzag Level Order Traversal	Solution	Medium
104. Maximum Depth of Binary Tree	Solution	Easy
105. Construct Binary Tree from Preorder and Inorder Traversal	Solution	Medium
108. Convert Sorted Array to Binary Search Tree	Solution	Easy
112. Path Sum	Solution	Easy
113. Path Sum II	Solution	Medium
114. Flatten Binary Tree to Linked List	Solution	Medium
116. Populating Next Right Pointers in Each Node	Solution	Medium
124. Binary Tree Maximum Path Sum	Solution	Hard
144. Binary Tree Preorder Traversal	Solution	Medium
173. Binary Search Tree Iterator	Solution	Medium
199. Binary Tree Right Side View	Solution	Medium
297. Serialize and Deserialize Binary Tree	Solution	Hard
235. Lowest Common Ancestor of a Binary Search Tree	Solution	Easy
236. Lowest Common Ancestor of a Binary Tree	Solution	Medium
257. Binary Tree Paths	Solution	Easy
617. Merge Two Binary Trees	Solution	Easy

Binary Search

Title	Solution	Difficulty
004. Median of Two Sorted Arrays	Solution	Hard
029. Divide Two Integers	Solution	Medium
033. Search in Rotated Sorted Array	Solution	Medium
034. Find First and Last Position of Element in Sorted Array	Solution	Medium
035. Search Insert Position	Solution	Easy
050. Pow(x, n)	Solution	Medium
069. Sqrt(x)	Solution	Easy
074. Search a 2D Matrix	Solution	Medium
162. Find Peak Element	Solution	Medium
240. Search a 2D Matrix II	Solution	Medium
300. Longest Increasing Subsequence	Solution	Medium
367. Valid Perfect Square	Solution	Easy

Linked List

Title	Solution	Difficulty
002. Add Two Numbers	Solution	Medium
019. Remove Nth Node From End of List	Solution	Medium
021. Merge Two Sorted Lists	Solution	Easy
024. Swap Nodes in Pairs	Solution	Medium
023. Merge k Sorted Lists	Solution	Hard
061. Rotate List	Solution	Medium
083. Remove Duplicates from Sorted List	Solution	Easy
141. Linked List Cycle	Solution	Easy
146. LRU Cache	Solution	Hard
148. Sort List	Solution	Medium
160. Intersection of Two Linked Lists	Solution	Easy
206. Reverse Linked List	Solution	Easy
234. Palindrome Linked List	Solution	Easy
369. Plus One Linked List	Solution	Medium
**Delete Node Greater than X	Solution	Easy
**Merge in Between.java	Solution	Easy

HashMap

Title	Solution	Difficulty
003. Longest Substring Without Repeating Characters	Solution	Medium
036. Valid Sudoku	Solution	Medium
049. Group Anagrams	Solution	Medium
076. Minimum Window Substring	Solution	Hard
146. LRU Cache	Solution	Hard
159. Longest Substring with At Most Two Distinct Characters	Solution	Hard
166. Fraction to Recurring Decimal	Solution	Medium
205. Isomorphic Strings	Solution	Easy
242. Valid Anagram	Solution	Easy
244. Shortest Word Distance II	Solution	Medium
249. Group Shifted Strings	Solution	Medium
336. Palindrome Pairs	Solution	Hard
340. Longest Substring with At Most K Distinct Characters	Solution	Hard
347. Top K Frequent Elements	Solution	Medium
359. Logger Rate Limiter	Solution	Easy
380. Insert Delete GetRandom O(1)	Solution	Medium
387. First Unique Character in a String	Solution	Easy
681. Next Closest Time	Solution	Medium
692. Top K Frequent Words	Solution	Medium
760. Find Anagram Mappings	Solution	Easy
763. Partition Labels	Solution	Medium
771. Jewels and Stones	Solution	Easy
781. Rabbits in Forest	Solution	Medium
811. Subdomain Visit Count	Solution	Easy
**Keyboard	Solution	Medium

Queue

Title	Solution	Difficulty
102. Binary Tree Level Order Traversal	Solution	Medium
207. Course Schedule	Java	Medium
239. Sliding Window Maximum	Solution	Hard
582. Kill Process	Solution	Medium

Heap

Title	Solution	Difficulty
215. Kth Largest Element in an Array	Solution	Medium
347. Top K Frequent Elements	Solution	Medium
373. Find K Pairs with Smallest Sums	Solution	Medium
378. Kth Smallest Element in a Sorted Matrix	Solution	Medium
632. Smallest Range	Solution	Hard
642. Design Search Autocomplete System	Solution	Hard
692. Top K Frequent Words	Solution	Medium
703. Kth Largest Element in a Stream	Solution	Easy
759. Employee Free Time	Solution	Hard

Two Pointers

Title	Solution	Difficulty
003. Longest Substring Without Repeating Characters	Solution	Medium
016. 3Sum Closest	Solution	Medium
026. Remove Duplicates from Sorted Array	Solution	Easy
031. Next Permutation	Solution	Medium
042. Trapping Rain Water	Solution	Hard
075. Sort Colors	Solution	Medium
088. Merge Sorted Array	Solution	Easy
159. Longest Substring with At Most Two Distinct Characters	Solution	Hard
167. Two Sum II - Input array is sorted	Solution	Easy
345. Reverse Vowels of a String	Solution	Easy
340. Longest Substring with At Most K Distinct Characters	Solution	Hard
632. Smallest Range	Solution	Hard
633. Sum of Square Numbers	Solution	Easy
763. Partition Labels	Solution	Medium
904. Fruit Into Baskets	Solution	Medium
*382. Triangle Count	Solution	Medium
*464. Sort Integers II	Solution	Easy
*609. Two Sum - Less than or equal to target	Solution	Medium

Math

Title	Solution	Difficulty
007. Reverse Integer	Solution	Easy
008. String to Integer (atoi)	Solution	Medium
009. Palindrome Number	Solution	Easy
012. Integer to Roman	Solution	Medium
013. Roman to Integer	Solution	Easy
029. Divide Two Integers	Solution	Medium
050. Pow(x, n)	Solution	Medium
136. Single Number	Solution	Easy
166. Fraction to Recurring Decimal	Solution	Medium
168. Excel Sheet Column Title	Solution	Easy
224. Basic Calculator I	Java	Hard
231. Power of Two	Solution	Easy
258. Add Digits	Solution	Easy
268. Missing Number	Solution	Easy
273. Integer to English Words	Solution	Hard
279. Perfect Squares	Solution	Medium
326. Power of Three	Solution	Easy
342. Power of Four	Solution	Easy
441. Arranging Coins	Solution	Easy
507. Perfect Number	Solution	Easy
633. Sum of Square Numbers	Solution	Easy
781. Rabbits in Forest	Solution	Medium
829. Consecutive Numbers Sum	Solution	Hard

Bit Manipulation

Title	Solution	Difficulty
231. Power of Two	Solution	Easy
751. IP to CIDR	Solution	Easy

Breadth-First Search

Title	Solution	Difficulty
116. Populating Next Right Pointers in Each Node	Solution	Medium
126. Word Ladder II	Solution	Hard
127. Word Ladder	Solution	Medium
128. Longest Consecutive Sequence	Solution	Hard
130. Surrounded Regions	Solution	Medium
200. Number of Islands	Solution	Medium
210. Course Schedule II	Solution	Medium
269. Alien Dictionary	Solution	Hard
329. Longest Increasing Path in a Matrix	Solution	Hard
490. The Maze	Solution	Medium
695. Max Area of Island	Solution	Easy
773. Sliding Puzzle	Solution	Hard
787. Cheapest Flights Within K Stops	[Solution]
(./LeetCode/787_Cheapest_Flights_Within_K_Stops.java)	Medium
815. Bus Routes	Solution	Hard

Depth-First Search

Title	Solution	Difficulty
101. Symmetric Tree	Solution	Easy
105. Construct Binary Tree from Preorder and Inorder Traversal	Solution	Medium
108. Convert Sorted Array to Binary Search Tree	Solution	Easy
126. Word Ladder II	Solution	Hard
131. Palindrome Partitioning	Solution	Medium
756. Pyramid Transition Matrix	Solution	Medium
490. The Maze	Solution	Medium

Backtracking

Title	Solution	Difficulty
017. Letter Combinations of a Phone Number	Solution	Medium
022. Generate Parentheses	Solution	Medium
039. Combination Sum	Solution	Medium
046. Permutations	Solution	Medium
047. Permutations II	Solution	Medium
131. Palindrome Partitioning	Solution	Medium
140. Word Break II	Solution	Hard
212. Word Search II	Solution	Hard

Stack

Title	Solution	Difficulty
032. Longest Valid Parentheses	Solution	Hard
094. Binary Tree Inorder Traversal	Solution	Medium
103. Binary Tree Zigzag Level Order Traversal	Solution	Medium
144. Binary Tree Preorder Traversal	Solution	Medium
150. Evaluate Reverse Polish Notation	Solution	Medium
155. Min Stack	Solution	Easy
173. Binary Search Tree Iterator	Solution	Medium
316. Remove Duplicate Letters	Solution	Hard
341. Flatten Nested List Iterator	Solution	Medium
739. Daily Temperatures	Solution	Medium
**Implement Stack By LinkedList	Solution	Easy

Dynamic Programming

Title	Solution	Difficulty
005. Longest Palindromic Substring	Solution	Medium
010. Regular Expression Matching	Solution	Hard
055. Jump Game	Solution	Medium
062. Unique Paths	Solution	Medium
064. Minimum Path Sum	Solution	Medium
070. Climbing Stairs	Solution	Easy
072. Edit Distance	Solution	Hard
091. Decode Ways	Solution	Medium
120. Triangle	Solution	Medium
131. Palindrome Partitioning	Solution	Medium
139. Word Break	Solution	Medium
140. Word Break II	Solution	Hard
152. Maximum Product Subarray	Solution	Medium
198. House Robber	Solution	Easy
213. House Robber II	Solution	Medium
221. Maximal Square	Solution	Medium
224. Basic Calculator I	Java	Hard
279. Perfect Squares	Solution	Medium
312. Burst Balloons	Solution	Hard
329. Longest Increasing Path in a Matrix	Solution	Hard
647. Palindromic Substrings	Solution	Medium
688. Knight Probability in Chessboard	Solution	Medium
746. Min Cost Climbing Stairs	Solution	Easy
*109. Triangle	Solution	Easy

Sort

Title	Solution	Difficulty
023. Merge k Sorted Lists	Solution	Hard
049. Group Anagrams	Solution	Medium
056. Merge Intervals	Solution	Medium
148. Sort List	Solution	Medium
179. Largest Number	Solution	Medium
218. The Skyline Problem	Solution	Hard
252. Meeting Rooms	Solution	Easy
253. Meeting Rooms II	Solution	Medium
280. Wiggle Sort	Solution	Medium
295. Find Median from Data Stream	Solution	Hard
324. Wiggle Sort II	Solution	Hard
*464. Sort Integers II	Solution	Easy

Greedy

Title	Solution	Difficulty
045. Jump Game II	Solution	Hard
134. Gas Station	Solution	Medium
406. Queue Reconstruction by Height	Solution	Medium
765. Couples Holding Hands	Solution	Hard
787. Cheapest Flights Within K Stops	Solution	Medium

Graph

Title	Solution	Difficulty
133. Clone Graph	Solution	Medium
207. Course Schedule	Java	Medium
210. Course Schedule II	Solution	Medium
269. Alien Dictionary	Solution	Hard
582. Kill Process	Solution	Medium

Trie

Title	Solution	Difficulty
208. Implement Trie (Prefix Tree)	Solution	Medium
421. Maximum XOR of Two Numbers in an Array)	Solution	Medium
642. Design Search Autocomplete System	Solution	Hard

Union Find

Title	Solution	Difficulty
211. Add and Search Word - Data structure design	Solution	Medium
212. Word Search II	Solution	Hard
261. Graph Valid Tree	Solution	Medium
305. Number of Islands II	Solution	Hard
425. Word Squares	Solution	Hard
684. Redundant Connection	Solution	Medium
721. Accounts Merge	Solution	Medium
737. Sentence Similarity II	Solution	Medium
765. Couples Holding Hands	Solution	Hard
*589. Connecting Graph	Solution	Medium
*590. Connecting Graph II	Solution	Medium
*591. Connecting Graph III	Solution	Medium

Design

Title	Solution	Difficulty
380. Insert Delete GetRandom O(1)	Solution	Medium
642. Design Search Autocomplete System	Solution	Hard
**Friends Graph	Solution	Easy

License

MIT