Solutions & Explanations

Browse 4,029+ detailed solutions with multiple approaches, code in Python, Java, C++ and more.

4,029 Solutions961 Easy2102 Medium966 Hard

Title	Difficulty	Acceptance	Topics	Solution
4. Median of Two Sorted Arrays	Hard	47.3%	Array Binary Search+1	Read
10. Regular Expression Matching	Hard	31.8%	Dynamic Programming Recursion+1	Read
23. Merge k Sorted Lists	Hard	60.3%	Divide and Conquer Heap (Priority Queue)+2	Read
25. Reverse Nodes in k-Group	Hard	66.8%	Linked List Recursion	Read
30. Substring with Concatenation of All Words	Hard	34.8%	Hash Table Sliding Window+1	Read
32. Longest Valid Parentheses	Hard	39.5%	Dynamic Programming Stack+1	Read
37. Sudoku Solver	Hard	65.4%	Array Backtracking+2	Read
41. First Missing Positive	Hard	43.8%	Array Hash Table	Read
42. Trapping Rain Water	Hard	68.2%	Array Dynamic Programming+3	Read
44. Wildcard Matching	Hard	32.8%	Dynamic Programming Greedy+2	Read
51. N-Queens	Hard	76.3%	Array Backtracking	Read
52. N-Queens II	Hard	78.9%	Backtracking	Read
60. Permutation Sequence	Hard	54.3%	Math Recursion	Read
65. Valid Number	Hard	23.3%	String	Read
68. Text Justification	Hard	51.8%	Array Simulation+1	Read
76. Minimum Window Substring	Hard	48.3%	Hash Table Sliding Window+1	Read
84. Largest Rectangle in Histogram	Hard	50.7%	Array Monotonic Stack+1	Read
85. Maximal Rectangle	Hard	59.5%	Array Dynamic Programming+3	Read
87. Scramble String	Hard	45.3%	Dynamic Programming String	Read
115. Distinct Subsequences	Hard	54.1%	Dynamic Programming String	Read
123. Best Time to Buy and Sell Stock III	Hard	54.5%	Array Dynamic Programming	Read
124. Binary Tree Maximum Path Sum	Hard	42.7%	Binary Tree Depth-First Search+2	Read
126. Word Ladder II	Hard	27.7%	Backtracking Breadth-First Search+2	Read
127. Word Ladder	Hard	46.3%	Breadth-First Search Hash Table+1	Read
132. Palindrome Partitioning II	Hard	37.9%	Dynamic Programming String	Read
135. Candy	Hard	49.3%	Array Greedy	Read
140. Word Break II	Hard	55.8%	Array Backtracking+5	Read
149. Max Points on a Line	Hard	31.0%	Array Geometry+2	Read
154. Find Minimum in Rotated Sorted Array II	Hard	46.6%	Array Binary Search	Read
158. Read N Characters Given read4 II - Call Multiple Times	Hard	43.2%	Array Interactive+1	Read
174. Dungeon Game	Hard	42.2%	Array Dynamic Programming+1	Read
185. Department Top Three Salaries	Hard	55.8%	Database	Read
188. Best Time to Buy and Sell Stock IV	Hard	50.9%	Array Dynamic Programming	Read
212. Word Search II	Hard	38.8%	Array Backtracking+3	Read
214. Shortest Palindrome	Hard	42.7%	Hash Function Rolling Hash+2	Read
218. The Skyline Problem	Hard	45.7%	Array Binary Indexed Tree+5	Read
220. Contains Duplicate III	Hard	25.2%	Array Bucket Sort+3	Read
224. Basic Calculator	Hard	46.7%	Math Recursion+2	Read
233. Number of Digit One	Hard	39.9%	Dynamic Programming Math+1	Read
239. Sliding Window Maximum	Hard	49.1%	Array Heap (Priority Queue)+3	Read
248. Strobogrammatic Number III	Hard	42.3%	Array Recursion+1	Read
262. Trips and Users	Hard	36.7%	Database	Read
265. Paint House II	Hard	57.0%	Array Dynamic Programming	Read
269. Alien Dictionary	Hard	37.1%	Array Breadth-First Search+4	Read
272. Closest Binary Search Tree Value II	Hard	61.1%	Binary Search Tree Binary Tree+5	Read
273. Integer to English Words	Hard	34.9%	Math Recursion+1	Read
282. Expression Add Operators	Hard	43.5%	Backtracking Math+1	Read
295. Find Median from Data Stream	Hard	54.9%	Data Stream Design+3	Read
296. Best Meeting Point	Hard	61.1%	Array Math+2	Read
297. Serialize and Deserialize Binary Tree	Hard	61.1%	Binary Tree Breadth-First Search+4	Read

#4Hard

Median of Two Sorted Arrays

ArrayBinary SearchDivide and Conquer

Acceptance: 47.3%

#10Hard

Regular Expression Matching

Dynamic ProgrammingRecursionString

Acceptance: 31.8%

#23Hard

Merge k Sorted Lists

Divide and ConquerHeap (Priority Queue)Linked List+1

Acceptance: 60.3%

#25Hard

Reverse Nodes in k-Group

Linked ListRecursion

Acceptance: 66.8%

#30Hard

Substring with Concatenation of All Words

Hash TableSliding WindowString

Acceptance: 34.8%

#32Hard

Longest Valid Parentheses

Dynamic ProgrammingStackString

Acceptance: 39.5%

#37Hard

Sudoku Solver

ArrayBacktrackingHash Table+1

Acceptance: 65.4%

#41Hard

First Missing Positive

ArrayHash Table

Acceptance: 43.8%

#42Hard

Trapping Rain Water

ArrayDynamic ProgrammingMonotonic Stack+2

Acceptance: 68.2%

#44Hard

Wildcard Matching

Dynamic ProgrammingGreedyRecursion+1

Acceptance: 32.8%

#51Hard

N-Queens

ArrayBacktracking

Acceptance: 76.3%

#52Hard

N-Queens II

Backtracking

Acceptance: 78.9%

#60Hard

Permutation Sequence

MathRecursion

Acceptance: 54.3%

#65Hard

Valid Number

String

Acceptance: 23.3%

#68Hard

Text Justification

ArraySimulationString

Acceptance: 51.8%

#76Hard

Minimum Window Substring

Hash TableSliding WindowString

Acceptance: 48.3%

#84Hard

Largest Rectangle in Histogram

ArrayMonotonic StackStack

Acceptance: 50.7%

#85Hard

Maximal Rectangle

ArrayDynamic ProgrammingMatrix+2

Acceptance: 59.5%

#87Hard

Scramble String

Dynamic ProgrammingString

Acceptance: 45.3%

#115Hard

Distinct Subsequences

Dynamic ProgrammingString

Acceptance: 54.1%

#123Hard

Best Time to Buy and Sell Stock III

ArrayDynamic Programming

Acceptance: 54.5%

#124Hard

Binary Tree Maximum Path Sum

Binary TreeDepth-First SearchDynamic Programming+1

Acceptance: 42.7%

#126Hard

Word Ladder II

BacktrackingBreadth-First SearchHash Table+1

Acceptance: 27.7%

#127Hard

Word Ladder

Breadth-First SearchHash TableString

Acceptance: 46.3%

#132Hard

Palindrome Partitioning II

Dynamic ProgrammingString

Acceptance: 37.9%

#135Hard

Candy

ArrayGreedy

Acceptance: 49.3%

#140Hard

Word Break II

ArrayBacktrackingDynamic Programming+4

Acceptance: 55.8%

#149Hard

Max Points on a Line

ArrayGeometryHash Table+1

Acceptance: 31.0%

#154Hard

Find Minimum in Rotated Sorted Array II

ArrayBinary Search

Acceptance: 46.6%

#158Hard

Read N Characters Given read4 II - Call Multiple Times

ArrayInteractiveSimulation

Acceptance: 43.2%

#174Hard

Dungeon Game

ArrayDynamic ProgrammingMatrix

Acceptance: 42.2%

#185Hard

Department Top Three Salaries

Database

Acceptance: 55.8%

#188Hard

Best Time to Buy and Sell Stock IV

ArrayDynamic Programming

Acceptance: 50.9%

#212Hard

Word Search II

ArrayBacktrackingMatrix+2

Acceptance: 38.8%

#214Hard

Shortest Palindrome

Hash FunctionRolling HashString+1

Acceptance: 42.7%

#218Hard

The Skyline Problem

ArrayBinary Indexed TreeDivide and Conquer+4

Acceptance: 45.7%

#220Hard

Contains Duplicate III

ArrayBucket SortOrdered Set+2

Acceptance: 25.2%

#224Hard

Basic Calculator

MathRecursionStack+1

Acceptance: 46.7%

#233Hard

Number of Digit One

Dynamic ProgrammingMathRecursion

Acceptance: 39.9%

#239Hard

Sliding Window Maximum

ArrayHeap (Priority Queue)Monotonic Queue+2

Acceptance: 49.1%

#248Hard

Strobogrammatic Number III

ArrayRecursionString

Acceptance: 42.3%

#262Hard

Trips and Users

Database

Acceptance: 36.7%

#265Hard

Paint House II

ArrayDynamic Programming

Acceptance: 57.0%

#269Hard

Alien Dictionary

ArrayBreadth-First SearchDepth-First Search+3

Acceptance: 37.1%

#272Hard

Closest Binary Search Tree Value II

Binary Search TreeBinary TreeDepth-First Search+4

Acceptance: 61.1%

#273Hard

Integer to English Words

MathRecursionString

Acceptance: 34.9%

#282Hard

Expression Add Operators

BacktrackingMathString

Acceptance: 43.5%

#295Hard

Find Median from Data Stream

Data StreamDesignHeap (Priority Queue)+2

Acceptance: 54.9%

#296Hard

Best Meeting Point

ArrayMathMatrix+1

Acceptance: 61.1%

#297Hard

Serialize and Deserialize Binary Tree

Binary TreeBreadth-First SearchDepth-First Search+3

Acceptance: 61.1%

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