LeetCode (709/2356) → Easy 227--Medium 383--Hard 97

Algorithm exercises 🚨🚨🚨

my homepage in leetcode.com

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the following problem is choose by:

the problem of Daily Challenges and Weekly Contest, and the similar problem on leetcode.com and leetcode-cn.com.

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Book

• Algorithms, 4TH

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----SameQuestionGroup----

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Tag	Progress
Array	141/287
Backtracking	28/57
Binary Indexed Tree	2/6
Binary Search	42/91
Binary Search Tree	2/15
Bit Manipulation	21/54
Brainteaser	4/7
Breadth-first Search	24/74
Concurrency	1/9
Counting	25/86
Database	3/112
Depth-first Search	61/134
Desigin	11/55
Divide and Conquer	8/19
Dynamic Programming	83/222
Geometry	3/9
Graph	18/47
Greedy	39/100
Hash Table	50/133
Heap	10/35
Linked List	30/39
Math	47/122
Memoization	1/1
Minimax	3/8
Ordered Map	3/12
Queue	3/9
Recursion	5/15
Rejection Sampling	1/2
Random	3/6
Rolling Hash	1/3
Segment Tree	4/14
Sliding Window	7/25
Sort	32/52
Stack	26/57
String	87/199
Topological Sort	4/7
Tree	81/148
Trie	8/17
Two Pointers	38/60
Union Find	12/32
other	8/?

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Title	Tags	Difficulty
1. Two Sum	Array HashTable	Easy
2. Add Two Numbers	Math LinkedList	Medium
3.Longest Substring Without Repeating Characters	String Two Pointers HashTables Sliding Window	Medium
4. Median of Two Sorted Arrays.md🚨	Array Binary Serach Divide and Conquer	Hard
5. Longest Palindromic Substring🚨	String Dynamic Programming	Medium
6. ZigZag Conversion	String	Medium
7. Reverse Integer	Math	Easy
8. String to Integer (atoi)	String Math	Medium
9. Palindrome Number	Math	Easy
10. Regular Expression Matching🚨	String Dynamic Programming BackTracking	Hard
11. Container With Most Water	Array Two Pointer	Medium
12. Integer to Roman	Math String	Medium
13. Roman to Integer	Math String	Easy
14. Longest Common Prefix	String	Easy
15. 3Sum 🚨	Array Two Pointer	Medium
16. 3Sum Closest	Array Two Pointer	Medium
17. Letter Combinations of a Phone Number	String BackTracking	Medium
18. 4Sum 🚨	Array Two Pointer HashTable	Medium
19. Remove Nth Node From End of List	LinkedList Two Pointers	Medium
20. Valid Parentheses	String Stack	Easy
21. Merge Two Sorted Lists	LinkedList	Easy
22. Generate Parentheses	String BackTracking	Medium
23.Merge k Sorted Lists	LinkedList Divide and Conquer Heap	Hard
24. Swap Nodes in Pairs	LinkedList	Medium
25. Reverse Nodes in k-Group	LinkedList	Hard
26. Remove Duplicates from Sorted Array	Array Two Pointer	Easy
27. Remove Element	Array Two Pointer	Easy
28. Implement strStr()	String Two Pointers	Easy
31. Next Permutation 🚨	Array	Medium
32. Longest Valid Parentheses🚨	String Dynamic Programming	Hard
33. Search in Rotated Sorted Array 🚨	Array Binary Serach	Medium
34. Find First and Last Position of Element in Sorted Array 🚨	Array Binary Serach	Medium
35. Search Insert Position	Array Binary Serach	Easy
36. Valid Sudoku	HashTable	Medium
37. Sudoku Solver	HashTable Backtracking	Hard
38. Count and Say	String	Easy
39. Combination Sum	Array Backtracking	Medium
40. Combination Sum II	Array Backtracking	Medium
41. First Missing Positive🚨	Array	Hard
43. Multiply Strings	Math String	Medium
44. Wildcard Matching	String Dynamic Programming Greedy Backtracking	Hard
46. Permutations	Backtracking	Medium
47. Permutations II	Backtracking	Medium
48. Rotate Image	Array	Medium
49. Group Anagrams	String HashTable	Medium
50. Pow(x, n)	Math BinarySearch	Medium
51. N-Queens	Backtracking	Hard
52. N-Queens II	Backtracking	Hard
53. Maximum Subarray	Array Divide and Conquer Dynamic Programming	Easy
54. Spiral Matrix	Array	Medium
56. Merge Intervals	Sort Array	Medium
57. Insert Interval	Array Sort	Medium
58. Length of Last Word	String	Easy
59. Spiral Matrix II	Array	Medium
60. Permutation Sequence	Math Backtracking	Hard
61. Rotate List	LinkedList Two Pointers	Medium
62. Unique Paths	Array Dynamic Programming	Medium
63. Unique Paths II	Array Dynamic Programming	Medium
64. Minimum Path Sum	Array Dynamic Programming	Medium
65. Valid Number	String Math	Hard
66. Plus One	Array	Easy
67. Add Binary	Math String	Easy
70. Climbing Stairs	Dynamic Programming	Easy
73. Set Matrix Zeroes	Array	Medium
74. Search a 2D Matrix	Array Binary Search	Medium
75. Sort Colors	Array Two Pointer Sort	Medium
77. Combinations	Backtracking	Medium
78. Subsets	Array Backtracking Bit Manipulation	Medium
79. Word Search	Array BackTracking	Medium
80. Remove Duplicates from Sorted Array II	Array Two Pointers	Medium
81. Search in Rotated Sorted Array II	Array BinarySearch	Medium
82. Remove Duplicates from Sorted List II	LinkedList	Medium
83. Remove Duplicates from Sorted List	LinkedList	Easy
84. Largest Rectangle in Histogram 🚨🚨	Array Stack	Hard
86. Partition List	LinkedList Two Pointers	Medium
88. Merge Sorted Array	Array Two Pointers	Easy
91. Decode Ways	Dynamic Programming String	Medium
92. Reverse Linked List II	LinkedList	Medium
93. Restore IP Addresses	String Backtracking	Medium
94. Binary Tree Inorder Traversal	Stack HashTable Tree	Medium
95. Unique Binary Search Trees II	Tree Dynamic Programming	Medium
96. Unique Binary Search Trees	Tree Dynamic Programming	Medium
97. Interleaving String	String Dynamic Programming	Hard
98. Validate Binary Search Tree	Tree DFS	Medium
99. Recover Binary Search Tree	DFS Tree	Hard
100. Same Tree	DFS Tree	Easy
101. Symmetric Tree	DFS BFS Tree	Easy
102. Binary Tree Level Order Traversal	Tree BFS	Medium
103. Binary Tree Zigzag Level Order Traversal	Tree BFS Stack	Medium
104. Maximum Depth of Binary Tree	DFS Tree	Easy
105. Construct Binary Tree from Preorder and Inorder Traversal	Tree Array DFS	Medium
106. Construct Binary Tree from Inorder and Postorder Traversal	Tree Array DFS	Medium
107. Binary Tree Level Order Traversal II	Tree BFS	Easy
108. Convert Sorted Array to Binary Search Tree	DFS Tree	Easy
109. Convert Sorted List to Binary Search Tree	LinkedList DFS	Medium
110. Balanced Binary Tree	Tree DFS	Easy
111. Minimum Depth of Binary Tree	Tree DFS BFS	Easy
112. Path Sum	DFS Tree	Easy
113. Path Sum II	Tree DFS	Medium
114. Flatten Binary Tree to Linked List	Tree DFS	Medium
116. Populating Next Right Pointers in Each Node	DFS Tree	Medium
117. Populating Next Right Pointers in Each Node II	Tree DFS	Medium
118. Pascal's Triangle	Array	Easy
119. Pascal's Triangle II	Array	Easy
120. Triangle	Array Dynamic Programming	Medium
121. Best Time to Buy and Sell Stock	Array Dynamic Programming	Easy
122. Best Time to Buy and Sell Stock II	Array Greedy	Easy
123. Best Time to Buy and Sell Stock III	Array Dynamic Programming	Hard
124. Binary Tree Maximum Path Sum	DFS Tree	Hard
125. Valid Palindrome	String Two Pointer	Easy
126. Word Ladder II 🚨	Array Backtracking String BFS	Hard
127. Word Ladder 🚨	BFS	Medium
128. Longest Consecutive Sequence 🚨	Array Union Find	Hard
129. Sum Root to Leaf Numbers	DFS Tree	Medium
130. Surrounded Regions	DFS BFS Union Find	Medium
131. Palindrome Partitioning	DynamicProgramming Backtracking DFS	Medium
132. Palindrome Partitioning II	Dynamic Programming	Hard
133. Clone Graph	DFS BFS Graph	Medium
134. Gas Station	Greedy	Medium
136. Single Number	HashTable Bit Manipulation	Easy
137. Single Number II	Bit Manipulation	Medium
138. Copy List with Random Pointer	LinkedList HashTable	Medium
139. Word Break	Dynamic Programming	Medium
140. Word Break II	Dynamic Programming Backtracking	Hard
141. Linked List Cycle	LinkedList Two Pointers	Easy
142. Linked List Cycle II	LinkedList Two Pointers	Medium
143. Reorder List	LinkedList	Medium
144. Binary Tree Preorder Traversal	Stack Tree	Medium
145. Binary Tree Postorder Traversal	Tree Stack	Medium
147. Insertion Sort List	Sort LinkedList	Medium
148. Sort List	Sort LinkedList	Medium
150. Evaluate Reverse Polish Notation	Stack	Medium
151. Reverse Words in a String	String	Medium
152. Maximum Product Subarray 🚨🚨	Array Dynamic Programming	Medium
153. Find Minimum in Rotated Sorted Array	Array BinarySearch	Medium
154. Find Minimum in Rotated Sorted Array II	Array BinarySearch	Hard
155. Min Stack	Stack Design	Easy
162. Find Peak Element	Array BinarySearch	Medium
165. Compare Version Numbers	String	Medium
167. Two Sum II - Input array is sorted	Array Two pointers Binary Search	Easy
169. Majority Element	Array Divide and Conquer Bit Manipulation	Easy
171. Excel Sheet Column Number	Math	Easy
173. Binary Search Tree Iterator	Tree Stack Design	Medium
174. Dungeon Game	Dynamic Programming Binary Search	Hard
179. Largest Number	Sort	Medium
187. Repeated DNA Sequences	HashTable Bit Manipulation	Medium
188. Best Time to Buy and Sell Stock IV	Dynamic Programming	Hard
189. Rotate Array	Array	Easy
190. Reverse Bits	Bit Manipulation	Easy
191. Number of 1 Bits	Bit Manipulation	Easy
198. House Robber	Dynamic Programming	Easy
201. Bitwise AND of Numbers Range	Bit Manipulation	Medium
203. Remove Linked List Elements	LinkedList	Easy
204. Count Primes	Math HashTable	Easy
206. Reverse Linked List	LinkedList	Easy
207. Course Schedule	DFS BFS Graph Topological Sort	Medium
208. Implement Trie (Prefix Tree)	Trie Design	Medium
209. Minimum Size Subarray Sum	Array Two Pointer Binary Search	Medium
210. Course Schedule II	DFS BFS Graph Topological Sort	Medium
211. Add and Search Word - Data structure design	Backtacking Design Trie	Medium
212. Word Search II	Trie Backtracking	Hard
213. House Robber II	Dynamic Programming	Medium
214. Shortest Palindrome 🚨🚨🚨	String	Hard
215. Kth Largest Element in an Array 🚨	Divide and Conquer Heap	Medium
216. Combination Sum III	Array Backtracking	Medium
217. Contains Duplicate	Array HashTable	Easy
220. Contains Duplicate III	Sort Ordered Map	Medium
221. Maximal Square	Dynamic Programming	Medium
222. Count Complete Tree Nodes	Tree Binary Search	Medium
226. Invert Binary Tree	Tree	Easy
227. Basic Calculator II	String Stack	Medium
228. Summary Ranges	Array	Easy
229. Majority Element II 🚨	Array	Medium
230. Kth Smallest Element in a BST	Binary Search Tree	Medium
231. Power of Two	Math Bit Manipulation	Easy
232. Implement Queue using Stacks	Stack Design	Easy
234. Palindrome Linked List	LinkedList Two Pointers	Easy
235. Lowest Common Ancestor of a Binary Search Tree	Tree	Easy
236. Lowest Common Ancestor of a Binary Tree	Tree	Medium
237. Delete Node in a Linked List	LinkedList	Easy
238. Product of Array Except Self	Array	Medium
240. Search a 2D Matrix II 🚨	BinarySearch Divide and Conquer	Medium
242. Valid Anagram	HsahTable Sort	Easy
257. Binary Tree Paths	Tree DFS	Easy
258. Add Digits	Math	Easy
260. Single Number III	Bit Manipulation	Medium
263. Ugly Number	Math	Easy
264. Ugly Number II	Math Dynamic Programming Heap	Medium
268. Missing Number	Array Math Bit Manipulation	Easy
274. H-Index	Sort HashTable	Medium
275. H-Index II	Binary Search	Medium
279. Perfect Squares 🚨	Dynamic Programming BFS Math	Medium
283. Move Zeroes	Array Two pointers	Easy
287. Find the Duplicate Number	Array Two pointers Binary Search	Medium
289. Game of Life	Array	Medium
290. Word Pattern	HashTable	Easy
292. Nim Game	Brainteaser Minimax	Easy
297. Serialize and Deserialize Binary Tree	Tree Design	Hard
299. Bulls and Cows	HashTable	Medium
300. Longest Increasing Subsequence	Binary Search Dynamic Programming	Medium
303. Range Sum Query - Immutable	Dynamic Programming	Easy
307. Range Sum Query - Mutable	Binary Indexed Tree Segment Tree	Medium
309. Best Time to Buy and Sell Stock with Cooldown 🚨	Dynamic Programming	Medium
310. Minimum Height Trees	BFS Graph	Medium
312. Burst Balloons 🚨	Divide and Conquer Dynamic Programming	Hard
315. Count of Smaller Numbers After Self	Binary Search Binary Indexed Tree Divide and Conquer Sort Segment Tree	Hard
316. Remove Duplicate Letters	String Stack Greedy	Medium
319. Bulb Switcher	Math Brainteaser	Medium
322. Coin Change 🚨	Dynamic Programming	Medium
328. Odd Even Linked List	LinkedList	Medium
329. Longest Increasing Path in a Matrix	DFS TopologicalSort Memoization	Hard
330. Patching Array 🚨🚨🚨	Greedy	Hard
332. Reconstruct Itinerary 🚨	DFS Graph	Medium
336. Palindrome Pairs 🚨🚨🚨	HashTable String Trie	Hard
337. House Robber III	Tree DFS	Medium
338. Counting Bits	Dynamic Programming Bit Manipulation	Medium
341. Flatten Nested List Iterator	Stack Design	Medium
342. Power of Four	Bit Manipulation	Easy
343. Integer Break	Math Dynamic Programming	Medium
344. Reverse String	String Two Pointers	Easy
347. Top K Frequent Elements	HashTable Heap	Medium
349. Intersection of Two Arrays	Binary Search Two Pointers HashTable Sort	Easy
350. Intersection of Two Arrays II	HashTable Two Pointers BinarySearch Sort	Easy
368. Largest Divisible Subset	Dynamic Programming Math	Medium
376. Wiggle Subsequence	Dynamic Programming Greedy	Medium
378. Kth Smallest Element in a Sorted Matrix	Binary Search Heap	Medium
382. Linked List Random Node	Reservoir Sampling	Medium
387. First Unique Character in a String	HashTable String	Easy
389. Find the Difference	HashTable Bit Manipulation	Easy
392. Is Subsequence	Binary Search Dynamic Programming Greedy	Easy
394. Decode String	DFS Stack	Medium
399. Evaluate Division 🚨	UnionFind Graph	Medium
400. Nth Digit	Math	Medium
402. Remove K Digits	Stack Greedy	Medium
404. Sum of Left Leaves	Tree	Easy
406. Queue Reconstruction by Height	Greedy	Medium
409. Longest Palindrome	HashTable	Easy
410. Split Array Largest Sum	Binary Search Dynamic Programming	Hard
412. Fizz Buzz	other	Easy
415. Add Strings	String	Easy
421. Maximum XOR of Two Numbers in an Array 🚨	Bit Manipulation Trie	Medium
424. Longest Repeating Character Replacement 🚨	Two Pointers Sliding Windows	Medium
429. N-ary Tree Level Order Traversal	BFS Tree	Medium
430. Flatten a Multilevel Doubly Linked List	LinkedList DFS	Medium
435. Non-overlapping Intervals 🚨	Greedy	Medium
436. Find Right Interval	Binary Search	Medium
437. Path Sum III	Tree	Medium
441. Arranging Coins	Math BinarySearch	Easy
442. Find All Duplicates in an Array	Array	Medium
445. Add Two Numbers II	LinkedList	Medium
448. Find All Numbers Disappeared in an Array	Array	Easy
450. Delete Node in a BST	Tree	Medium
452. Minimum Number of Arrows to Burst Balloons	Greedy Sort	Medium
454. 4Sum II	HashTable BinarySearch	Medium
456. 132 Pattern 🚨	Stack	Medium
459. Repeated Substring Pattern	String	Easy
460. LFU Cache	Design	Hard
461. Hamming Distance	Bit Manipulation	Easy
463. Island Perimeter	HashTable	Easy
468. Validate IP Address	String	Medium
470. Implement Rand10() Using Rand7()	Random Rejection Sampling	Medium
480. Sliding Window Median	Sliding Window	Hard
481. Magical String	other	Medium
485. Max Consecutive Ones	Array	Easy
486. Predict the Winner 🚨	Dynamic Programming MiniMax	Medium
491. Increasing Subsequences 🚨	DFS	Medium
494. Target Sum 🚨	Dynamic Programming DFS	Medium
495. Teemo Attacking	Array	Medium
496. Next Greater Element I	Stack	Easy
497. Random Point in Non-overlapping Rectangles	Random Binary Search	Medium
501. Find Mode in Binary Search Tree	Tree	Easy
503. Next Greater Element II	Stack	Medium
507. Perfect Number	Math	Easy
509. Fibonacci Number	Array	Easy
513. Find Bottom Left Tree Value	DFS BFS Tree	Medium
515. Find Largest Value in Each Tree Row	DFS BFS Tree	Medium
518. Coin Change 2	Dynamic Programming	Medium
520. Detect Capital	String	Easy
521. Longest Uncommon Subsequence I	String	Easy
523. Continuous Subarray Sum 🚨	Math Dynamic Programming	Medium
524. Longest Word in Dictionary through Deleting	Two Pointers Sort	Medium
525. Contiguous Array 🚨	HashTable	Medium
528. Random Pick with Weight 🚨	Random BinarySerach	Medium
529. Minesweeper	DFS BFS	Medium
530. Minimum Absolute Difference in BST	Tree	Easy
535. Encode and Decode TinyURL	Math HashTable	Medium
537. Complex Number Multiplication	Math String	Medium
538. Convert BST to Greater Tree	Tree	Medium
539. Minimum Time Difference	String	Medium
543. Diameter of Binary Tree	Tree	Easy
546. Remove Boxes 🚨🚨🚨	Dynamic Programming DFS	Hard
547. Friend Circles	DFS UnionFind	Medium
556. Next Greater Element III	String	Medium
557. Reverse Words in a String III	String	Easy
559. Maximum Depth of N-ary Tree	DFS BFS Tree	Easy
561. Array Partition I	Array	Easy
563. Binary Tree Tilt	Tree DFS Recursion	Easy
565. Array Nesting	Array	Medium
566. Reshape the Matrix	Array	Easy
572. Subtree of Another Tree	Tree	Easy
581. Shortest Unsorted Continuous Subarray	Array	Easy
589. N-ary Tree Preorder Traversal	Tree	Easy
593. Valid Square	Math	Medium
594. Longest Harmonious Subsequence	HashTable	Easy
595. Big Countries	Database	Easy
617. Merge Two Binary Trees	Tree	Easy
621. Task Scheduler	Array Greedy Queue	Medium
627. Swap Salary	Datebase	Easy
628. Maximum Product of Three Numbers	Array Math	Easy
630. Course Schedule III	Greedy	Hard
637. Average of Levels in Binary Tree	Tree	Easy
643. Maximum Average Subarray I	Array	Easy
645. Set Mismatch	Math HashTable	Easy
646. Maximum Length of Pair Chain	Dynamic Programming	Medium
647. Palindromic Substrings	String Dynamic Programming	Medium
649. Dota2 Senate	Greedy	Medium
654.Maximum Binary Tree	Tree	Medium
657. Robot Return to Origin	String	Easy
661. Image Smoother	Array	Easy
662. Maximum Width of Binary Tree	Tree	Medium
667. Beautiful Arrangement II	Array	Medium
669. Trim a Binary Search Tree	Tree Recursion	Medium
671. Second Minimum Node In a Binary Tree	Tree DFS Binary Tree	Easy
673. Number of Longest Increasing Subsequence 🚨	Dynamic Programming	Medium
674. Longest Continuous Increasing Subsequence	Array	Easy
679. 24 Game 🚨	DFS	Hard
680. Valid Palindrome II	String	Easy
684. Redundant Connection	Tree Union Find Graph	Medium
685. Redundant Connection II	Tree Union Find Graph DFS	Hard
692. Top K Frequent Words	HashTable Heap Trie	Medium
695. Max Area of Island	Array DFS	Medium
696. Count Binary Substrings	String	Easy
697. Degree of an Array	Array	Easy
700. Search in a Binary Search Tree	Tree	Easy
701. Insert into a Binary Search Tree	Tree	Medium
704. Binary Search	Binary Search	Easy
705. Design HashSet	HashTable Design	Easy
709.To Lower Case	String	Easy
713. Subarray Product Less Than K	Array Two Pointers	Medium
714. Best Time to Buy and Sell Stock with Transaction Fee	Array Dynamic Programming Greedy	Medium
717. 1-bit and 2-bit Characters	Array	Easy
718. Maximum Length of Repeated Subarray	Array BinarySearch HashTable Dynamic Programming	Medium
720. Longest Word in Dictionary	HashTable Trie	Easy
721. Accounts Merge	DFS UnionFind	Medium
724. Find Pivot Index	Array	Easy
725. Split Linked List in Parts	LinkedList	Medium
726. Number of Atoms	HashTable Stack Recursion	Hard
728. Self Dividing Numbers	Math	Easy
733. Flood Fill	DFS	Easy
735. Asteroid Collision	Stack	Medium
738. Monotone Increasing Digits	Greedy	Medium
739. Daily Temperatures	Stack HashTable	Medium
741. Cherry Pickup 🚨🚨🚨	Dynamic Programming	Hard
746. Min Cost Climbing Stairs	Array Dynamic Programming	Easy
754. Reach a Number 🚨	Math	Medium
763. Partition Labels	Greedy Two Pointers	Medium
766. Toeplitz Matrix	Array	Easy
767. Reorganize String	String Heap Greedy Sort	Medium
768. Max Chunks To Make Sorted II	Array	Hard
769. Max Chunks To Make Sorted	Array	Medium
771. Jewels and Stones	HashTable	Easy
778. Swim in Rising Water 🚨	BinarySearch Heap DFS UnionFind	Hard
783. Minimum Distance Between BST Nodes	Tree Recursive	Easy
785. Is Graph Bipartite?	DFS BFS Graph	Medium
787. Cheapest Flights Within K Stops 🚨	Dynamic Programming DFS Heap	Medium
791. Custom Sort String	String	Medium
797. Al Paths From Source to Target	DFS	Medium
799. Champagne Tower	other	Medium
804. Unique Morse Code Words	String	Easy
807. Max Increase to Keep City Skyline	other	Medium
814. Binary Tree Pruning	Tree	Medium
817. Linked List Components	LinkedList	Medium
818. Race Car 🚨🚨🚨	Dynamic Programming Heap	Hard
824. Goat Latin	String	Easy
830. Positions of Large Groups	Array	Easy
832. Flipping an Image	Array	Easy
835. Image Overlap 🚨	Array	Medium
837. New 21 Game 🚨	Dynamic Programming	Medium
841. Keys and Rooms	DFS Graph	Medium
842. Split Array into Fibonacci Sequence	Backtracking Greedy String	Medium
844. Backspace String Compare	Two Pointers Stack	Easy
845. Longest Mountain in Array	Two Pointers	Medium
849. Maximize Distance to Closest Person	Array	Medium
852. Peak Index in a Mountain Array	Binary Search	Easy
856. Score of Parentheses	Array Stack	Medium
858. Mirror Reflection	Math	Medium
859. Buddy Strings	String	Easy
860. Lemonade Change	Greedy	Easy
861. Score After Flipping Matrix	Greedy	Medium
862. Shortest Subarray with Sum at Least K 🚨	Queue Binary Search	Hard
863. All Nodes Distance K in Binary Tree	Tree DFS BFS	Medium
867. Transpose Matrix	Array	Easy
869. Reordered Power of 2	Math	Medium
872. Leaf-Similar Trees	DFS Tree	Easy
875. Koko Eating Bananas	BinarySearch	Medium
876. Middle of the Linked List	LinkedList	Easy
877. Stone Game	Dynamic Programming MiniMax Math	Medium
881. Boats to Save People	Greedy Two Pointers	Medium
888. Fair Candy Swap	Array	Easy
889. Construct Binary Tree from Preorder and Postorder Traversal	Tree	Medium
890. Find and Replace Pattern	String	Medium
894. All Possible Full Binary Trees🚨	Tree Recursion	Medium
897. Increasing Order Search Tree	DFS Tree	Easy
902. Numbers At Most N Given Digit Set 🚨	Math Dynamic Programming	Hard
904. Fruit Into Baskets	Two Pointers	Medium
905. Sort Array By Parity	Array	Easy
912. Sort an Array	Sort	Medium
922. Sort Array By Parity II	Array Sort	Easy
923. 3Sum With Multiplicity 🚨	Two Pointer	Medium
925. Long Pressed Name	String Two Pointer	Easy
929. Unique Email Addresses	String	Easy
930. Binary Subarrays With Sum	Two Pointers HashTable	Medium
933. Number of Recent Calls	Queue	Easy
938. Range Sum of BST	Tree Recursion	Easy
941. Valid Mountain Array	Array	Easy
942. DI String Match	Math	Easy
943. Find the Shortest Superstring	Dynamic Programming	Hard
948. Bag of Tokens	Greedy	Medium
949. Largest Time for Given Digits	Math	Medium
950. Reveal Cards In Increasing Order	Array	Medium
952. Largest Component Size by Common Factor	Math Union Find	Hard
957. Prison Cells After N Days	HashTable	Medium
959. Regions Cut By Slashes	DFS Graph Union Find	Medium
961. N-Repeated Element in Size 2N Array	HashTable	Easy
965. Univalued Binary Tree	Tree	Easy
966. Vowel Spellchecker	HashTable String	Medium
967. Numbers With Same Consecutive Differences	Dynamic Programming	Medium
969. Pancake Sorting	Array Sort	Medium
973. K Closest Points to Origin	Divide and Conquer Heap Sort	Medium
974. Subarray Sums Divisible by K 🚨	Array HashTable	Medium
976. Largest Perimeter Triangle	Sort Math	Easy
977.Squares of a Sorted Array	Array TwoPointers	Easy
978. Longest Turbulent Subarray	Array Dynamic Programming Silding Window	Medium
979. Distribute Coins in Binary Tree	DFS Tree	Medium
980. Unique Paths III	DFS BackTracking	Hard
983. Minimum Cost For Tickets 🚨	Dynamic Programming	Medium
987. Vertical Order Traversal of a Binary Tree	Tree HashTable	Medium
989. Add to Array-Form of Integer	Array	Easy
990. Satisfiability of Equality Equations	Union Find Graph	Medium
992. Subarrays with K Different Integers	Two Pointers HashTable Sliding Window	Hard
994. Rotting Oranges	BFS	Medium
1000. Minimum Cost to Merge Stones 🚨	Dynamic Programming	Hard
1002. Find Common Characters	Array HashTable	Easy
1004. Max Consecutive Ones III	Two Pointers Sliding Window	Medium
1005. Maximize Sum Of Array After K Negations	Greedy	Easy
1007. Minimum Domino Rotations For Equal Row	Array Greedy	Medium
1008. Construct Binary Search Tree from Preorder Traversal	Tree	Medium
1011. Capacity To Ship Packages Within D Days	Array Binary Search	Medium
1013. Partition Array Into Three Parts With Equal Sum	Array	Easy
1014. Best Sightseeing Pair 🚨	Array	Medium
1015. Smallest Integer Divisible by K	Math	Medium
1018. Binary Prefix Divisible By 5	Array	Easy
1019. Next Greater Node In Linked List 🚨	LinkedList Stack	Medium
1021. Remove Outermost Parentheses	Stack	Easy
1022. Sum of Root To Leaf Binary Numbers	Tree	Easy
1024. Video Stitching	Dynamic Programming	Medium
1025. Divisor Game	Math Dynamic Programming	Easy
1026. Maximum Difference Between Node and Ancestor	DFS Tree	Medium
1028. Recover a Tree From Preorder Traversal	DFS Tree	Hard
1029. Two City Scheduling	Greedy	Medium
1030. Matrix Cells in Distance Order	Sort	Easy
1032. Stream of Characters	Trie	Hard
1038. Binary Search Tree to Greater Sum Tree	Binary Search Tree	Medium
1039. Minimum Score Triangulation of Polygon 🚨	Dynamic Programming	Medium
1041. Robot Bounded In Circle	Math	Medium
1044. Longest Duplicate Substring 🚨🚨🚨	Binary Search HashTable	Hard
1046. Last Stone Weight	Heap Greedy	Easy
1047. Remove All Adjacent Duplicates In String	Stack	Easy
1051. Height Checker	Array	Easy
1053. Previous Permutation With One Swap	Array Greedy	Medium
1079. Letter Tile Possibilities 🚨	BackTracking	Medium
1081. Smallest Subsequence of Distinct Characters	String Stack Greedy	Medium
1094. Car Pooling	Greedy	Medium
1095. Find in Mountain Array	Binary Search	Hard
1103. Distribute Candies to People	Math	Easy
1108.Defanging an IP Address	String	Easy
1109. Corporate Flight Bookings 🚨	Math Array	Medium
1110. Delete Nodes And Return Forest	DFS Tree	Medium
1115. Print FooBar Alternately	Concurrency	Medium
1122. Relative Sort Array	Array Sort	Easy
1128. Number of Equivalent Domino Pairs	Array	Easy
1130. Minimum Cost Tree From Leaf Values	Tree Stack Dynamic Programming	Medium
1137. N-th Tribonacci Number	Recursive	Easy
1140. Stone Game II 🚨	Dynamic Programming	Medium
1143. Longest Common Subsequence	Dynamic Programming	Medium
1155. Number of Dice Rolls With Target Sum	Dynamic Programming	Medium
1179. Reformat Department Table🚨	Datebase	Easy
1202. Smallest String With Swaps	Array UnionFind	Medium
1207. Unique Number of Occurrences	HashTable	Easy
1208. Get Equal Substrings Within Budget	Array Sliding Window	Medium
1217. Minimum Cost to Move Chips to The Same Position	Math Array Greedy	Easy
1221. Split a String in Balanced Strings	String	Easy
1234. Replace the Substring for Balanced String	String Two Pointers	Medium
1248. Count Number of Nice Subarrays	Two Pointers	Medium
1249. Minimum Remove to Make Valid Parentheses	String Stack	Medium
1252. Cells with Odd Values in a Matrix	Array	Easy
1261. Find Elements in a Contaminated Binary Tree	HashTable Tree	Medium
1266. Minimum Time Visiting All Points	Array Geometry	Easy
1281. Subtract the Product and Sum of Digits of an Integer	Math	Easy
1282. Group the People Given the Group Size They Belong To🚨	Greedy	Medium
1283. Find the Smallest Divisor Given a Threshold	Binary Search	Medium
1286. Iterator for Combination	Design Backtracking	Medium
1290.Convert Binary Number in a Linked List to Integer	LinkedList Bit Manipulation	Easy
1291. Sequential Digits	Backtracking	Medium
1300. Sum of Mutated Array Closest to Target	Array BinarySearch	Medium
1302. Deepest Leaves Sum	DFS Tree	Medium
1305. All Elements in Two Binary Search Trees	Sort Tree	Medium
1314. Matrix Block Sum	Dynamic Programming	Medium
1315. Sum of Nodes with Even-Valued Grandparent	DFS Tree	Medium
1319. Number of Operations to Make Network Connected	DFS BFS UnionFind	Medium
1329. Sort the Matrix Diagonally	Array Sort	Medium
1340. Jump Game V 🚨	Dynamic Programming	Hard
1344. Angle Between Hands of a Clock	Math	Medium
1356. Sort Integers by The Number of 1 Bits	Sort Bit Manipulation	Easy
1358. Number of Substrings Containing All Three Characters	String	Medium
1365. How Many Numbers Are Smaller Than the Current Number	Array HashTable	Easy
1370. Increasing Decreasing String	String Sort	Easy
1406. Stone Game III 🚨	Dynamic Programming	Hard
1419. Minimum Number of Frogs Croaking	String	Medium
1425. Constrained Subsequence Sum	Dynamic Programming	Hard
1431. Kids With the Greatest Number of Candies	Array	Easy
1437. Check If All 1's Are at Least Length K Places Away	Array	Easy
1446. Consecutive Characters	String	Easy
1450. Number of Students Doing Homework at a Given Time	Array	Easy
1451. Rearrange Words in a Sentence	String Sort	Medium
1452. People Whose List of Favorite Companies Is Not a Subset of Another List	String Sort	Medium
1455. Check If a Word Occurs As a Prefix of Any Word in a Sentence	String	Easy
1456. Maximum Number of Vowels in a Substring of Given Length	String Sliding Window	Medium
1457. Pseudo-Palindromic Paths in a Binary Tree	DFS Tree Bit Manipulation	Medium
1458. Max Dot Product of Two Subsequences 🚨	Dynamic Programming	Hard
1462. Course Schedule IV	Graph TopologicalSort	Medium
1464. Maximum Product of Two Elements in an Array	Array	Easy
1465. Maximum Area of a Piece of Cake After Horizontal and Vertical Cuts	DFS Tree	Medium
1466. Reorder Routes to Make All Paths Lead to the City Zero	DFS Tree	Medium
1470. Shuffle the Array	Array	Easy
1471. The k Strongest Values in an Array	Array Sort	Medium
1472. Design Browser History	Design	Medium
1473. Paint House III 🚨	Dynamic Programming	Hard
1480. Running Sum of 1d Array	Array	Easy
1481. Least Number of Unique Integers after K Removals	Array Sort	Medium
1482. Minimum Number of Days to Make m Bouquets 🚨🚨🚨	Binary Search Array	Medium
1483. Kth Ancestor of a Tree Node 🚨🚨	Dynamic Programming	Hard
1486. XOR Operation in an Array	Array Bit Manipulation	Easy
1487. Making File Names Unique	String HashTable	Medium
1488. Avoid Flood in The City	Array HashTable	Medium
1489. Find Critical and Pseudo-Critical Edges in Minimum Spanning Tree 🚨	DFS UnionFind	Hard
1491. Average Salary Excluding the Minimum and Maximum Salary	Array Sort	Easy
1492. The kth Factor of n	Math	Medium
1493. Longest Subarray of 1's After Deleting One Element	Array	Medium
1496. Path Crossing	String	Easy
1497. Check If Array Pairs Are Divisible by k	Array Math Greedy	Medium
1498. Number of Subsequences That Satisfy the Given Sum Condition 🚨	Sort Sliding Window	Medium
1499. Max Value of Equation 🚨	Array Sliding Window	Hard
1502. Can Make Arithmetic Progression From Sequence	Array Sort	Easy
1503. Last Moment Before All Ants Fall Out of a Plank	Array Brainteaser	Medium
1504. Count Submatrices With All Ones	Dynamic Programming	Medium
1505. Minimum Possible Integer After at Most K Adjacent Swaps On Digits 🚨	Greedy	Hard
1507. Reformat Date	String	Easy
1508. Range Sum of Sorted Subarray Sums	Array Sort	Medium
1509. Minimum Difference Between Largest and Smallest Value in Three Moves	Array Sort	Medium
1510. Stone Game IV	Dynamic Programming	Hard
1512. Number of Good Pairs	Array Math HashTable	Easy
1513. Number of Substrings With Only 1s	String Math	Medium
1514. Path with Maximum Probability 🚨🚨🚨	Graph	Medium
1515. Best Position for a Service Centre 🚨🚨	Geometry	Hard
1518. Water Bottles	Greedy	Easy
1519. Number of Nodes in the Sub-Tree With the Same Label	BFS DFS	Medium
1520. Maximum Number of Non-Overlapping Substrings 🚨🚨	Greedy	Hard
1521. Find a Value of a Mysterious Function Closest to Target 🚨🚨🚨	BinarySearch Segment Tree Bit Manipulation	Hard
1523. Count Odd Numbers in an Interval Range	Math	Easy
1524. Number of Sub-arrays With Odd Sum 🚨	Array Math	Medium
1525. Number of Good Ways to Split a String	String Bit Manipulation	Medium
1526. Minimum Number of Increments on Subarrays to Form a Target Array 🚨	Segment Tree	Hard
1528. Shuffle String	Sort	Easy
1529. Bulb Switcher IV	String	Medium
1530. Number of Good Leaf Nodes Pairs	Tree DFS	Medium
1531. String Compression II 🚨🚨🚨	String Dynamic Programming	Hard
1534. Count Good Triplets	Array	Easy
1535. Find the Winner of an Array Game	Array	Medium
1536. Minimum Swaps to Arrange a Binary Grid	Greedy	Medium
1537. Get the Maximum Score	Dynamic Programming	Hard
1539. Kth Missing Positive Number	Array HashTable	Easy
1540. Can Convert String in K Moves	String Greedy	Medium
1541. Minimum Insertions to Balance a Parentheses String	String Stack	Medium
1542. Find Longest Awesome Substring 🚨🚨🚨	String Bit Manipulation	Hard
1544. Make The String Great	String Stack	Easy
1545. Find Kth Bit in Nth Binary String	String	Medium
1546. Maximum Number of Non-Overlapping Subarrays With Sum Equals Target 🚨🚨	Dynamic Programming	Medium
1547. Minimum Cost to Cut a Stick 🚨🚨🚨	Dynamic Programming	Hard
1550. Three Consecutive Odds	Array	Easy
1551. Minimum Operations to Make Array Equal	Math	Medium
1552. Magnetic Force Between Two Balls	Array Binary Search	Medium
1553. Minimum Number of Days to Eat N Oranges	Dynamic Programming	Hard
1556. Thousand Separator	String	Easy
1557. Minimum Number of Vertices to Reach All Nodes	Grpah	Medium
1558. Minimum Numbers of Function Calls to Make Target Array	Greedy	Medium
1559. Detect Cycles in 2D Grid	DFS	Hard
1560. Most Visited Sector in a Circular Track	Array	Easy
1561. Maximum Number of Coins You Can Get	Sort	Medium
1562. Find Latest Group of Size M 🚨	Binary Search	Medium
1563. Stone Game V 🚨🚨🚨	Dynamic Programming	Hard
1566. Detect Pattern of Length M Repeated K or More Times	Array	Easy
1567. Maximum Length of Subarray With Positive Product	Greedy	Meidum
1568. Minimum Number of Days to Disconnect Island	Greedy	Hard
1569. Number of Ways to Reorder Array to Get Same BST 🚨🚨	Dynamic Programming	Hard
1572. Matrix Diagonal Sum	Array	Easy
1573. Number of Ways to Split a String	String	Medium
1574. Shortest Subarray to be Removed to Make Array Sorted	Array Binary Search	Medium
1575. Count All Possible Routes 🚨🚨🚨	Dynamic Programming	Hard
1576. Replace All ?'s to Avoid Consecutive Repeating Characters	String	Easy
1577. Number of Ways Where Square of Number Is Equal to Product of Two Numbers	HashTable Math	Medium
1578. Minimum Deletion Cost to Avoid Repeating Letters	Greedy	Medium
1579. Remove Max Number of Edges to Keep Graph Fully Traversable 🚨🚨🚨	Union Find	Hard
1582. Special Positions in a Binary Matrix	Array	Easy
1583. Count Unhappy Friends	Array	Medium
1584. Min Cost to Connect All Points	Union Find	Medium
1585. Check If String Is Transformable With Substring Sort Operations	String Greedy	Hard
1588. Sum of All Odd Length Subarrays	Array	Easy
1589. Maximum Sum Obtained of Any Permutation	Greedy	Medium
1590. Make Sum Divisible by P 🚨	Array Binary Search	Medium
1591. Strange Printer II 🚨🚨	Greedy	Hard
1592. Rearrange Spaces Between Words	String	Easy
1593. Split a String Into the Max Number of Unique Substrings	Backtracking	Medium
1594. Maximum Non Negative Product in a Matrix	Dynamic Programming Greedy	Medium
1595. Minimum Cost to Connect Two Groups of Points 🚨🚨	Dynamic Programming Graph	Hard
1598. Crawler Log Folder	Stack	Easy
1599. Maximum Profit of Operating a Centennial Wheel	Greedy	Medium
1600. Throne Inheritance	Tree Design	Medium
1601. Maximum Number of Achievable Transfer Requests 🚨🚨	Dynamic Programming	Hard
1603. Design Parking System	Design	Easy
1604. Alert Using Same Key-Card Three or More Times in a One Hour Period	String Ordered Map	Medium
1605. Find Valid Matrix Given Row and Column Sums	Greedy 🚨	Medium
1606. Find Servers That Handled Most Number of Requests 🚨🚨	Ordered Map	Hard
1608. Special Array With X Elements Greater Than or Equal X	Array	Easy
1609. Even Odd Tree	Tree	Medium
1610. Maximum Number of Visible Points	Two Pointers Geometry	Hard
1611. Minimum One Bit Operations to Make Integers Zero 🚨🚨	DynamicProgramming Bit Manipulation	Hard
1614. Maximum Nesting Depth of the Parentheses	String	Easy
1615. Maximal Network Rank	Graph	Medium
1616. Split Two Strings to Make Palindrome 🚨	String Two Pointers Greedy	Medium
1617. Count Subtrees With Max Distance Between Cities 🚨🚨	Backtracking	Hard
1636. Sort Array by Increasing Frequency	Sort Array	Easy
1637. Widest Vertical Area Between Two Points Containing No Points	Sort	Medium
1638. Count Substrings That Differ by One Character	String Rolling Hash Trie HashTable	Medium
1639. Number of Ways to Form a Target String Given a Dictionary	Dynamic Programming	Hard
1646. Get Maximum in Generated Array	Array	Easy
1647. Minimum Deletions to Make Character Frequencies Unique	Greedy Sort	Medium
1648. Sell Diminishing-Valued Colored Balls	Greedy Sort Math	Medium
1649. Create Sorted Array through Instructions	Binary Indexed Tree Segment Tree Ordered Map	Hard
1657. Determine if Two Strings Are Close	Medium	Medium
1662. Check If Two String Arrays are Equivalent	String	Easy
1663. Smallest String With A Given Numeric Value	Greedy	Medium
1664. Ways to Make a Fair Array	Greedy Dynamic Programming	Medium
1665. Minimum Initial Energy to Finish Tasks	Greedy	Hard
1668. Maximum Repeating Substring	String	Easy
1669. Merge In Between Linked Lists	LinkedList	Medium
1670. Design Front Middle Back Queue	LinkedList Design Dequeue	Medium
1671. Minimum Number of Removals to Make Mountain Array	Dynamic Programming	Hard
1678. Goal Parser Interpretation	String	Easy
1679. Max Number of K-Sum Pairs	HashTable	Medium
1680. Concatenation of Consecutive Binary Numbers	Math	Medium
1689. Partitioning Into Minimum Number Of Deci-Binary Numbers	Greedy	Medium
1704. Determine if String Halves Are Alike	String	Easy
1710. Maximum Units on a Truck	Sort Greedy Array	Easy
1720. Decode XORed Array	Bit Manipulation	Easy
1734. Decode XORed Permutation	Bit Manipulation	Medium
1790. Check if One String Swap Can Make Strings Equal	String	Easy
1791. Find Center of Star Graph	Graph	Mediun
1792. Maximum Average Pass Ratio	Heap	Mediun
1793. Maximum Score of a Good Subarray	Greedy	Hard
1796. Second Largest Digit in a String	String	Easy
1797. Design Authentication Manager	Design HashTable	Medium
1798. Maximum Number of Consecutive Values You Can Make	Greedy	Medium
1799. Maximize Score After N Operations 🚨🚨	Dynamic Programming Backtracking Recursion	Hard
1800. Maximum Ascending Subarray Sum	Two Pointers	Easy
1838. Frequency of the Most Frequent Element	Array Binary Search Greedy Sliding Window Sorting Prefix Sum	Medium
2351. First Letter to Appear Twice	String HashTable Counting	Easy
2352. Equal Row and Column Pairs	Array HashTable Matrix Simulation	Medium