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
82. Remove Duplicates from Sorted List II	Medium	52.2%	Linked List Two Pointers	Read
86. Partition List	Medium	62.0%	Linked List Two Pointers	Read
89. Gray Code	Medium	65.6%	Backtracking Bit Manipulation+1	Read
90. Subsets II	Medium	61.7%	Array Backtracking+1	Read
91. Decode Ways	Medium	38.3%	Dynamic Programming String	Read
92. Reverse Linked List II	Medium	52.4%	Linked List	Read
93. Restore IP Addresses	Medium	56.7%	Backtracking String	Read
95. Unique Binary Search Trees II	Medium	63.3%	Backtracking Binary Search Tree+3	Read
96. Unique Binary Search Trees	Medium	64.0%	Binary Search Tree Binary Tree+3	Read
97. Interleaving String	Medium	44.4%	Dynamic Programming String	Read
98. Validate Binary Search Tree	Medium	36.1%	Binary Search Tree Binary Tree+2	Read
99. Recover Binary Search Tree	Medium	60.9%	Binary Search Tree Binary Tree+2	Read
102. Binary Tree Level Order Traversal	Medium	73.5%	Binary Tree Breadth-First Search+1	Read
103. Binary Tree Zigzag Level Order Traversal	Medium	64.4%	Binary Tree Breadth-First Search+1	Read
105. Construct Binary Tree from Preorder and Inorder Traversal	Medium	69.1%	Array Binary Tree+3	Read
106. Construct Binary Tree from Inorder and Postorder Traversal	Medium	69.4%	Array Binary Tree+3	Read
107. Binary Tree Level Order Traversal II	Medium	69.0%	Binary Tree Breadth-First Search+1	Read
109. Convert Sorted List to Binary Search Tree	Medium	67.4%	Binary Search Tree Binary Tree+3	Read
113. Path Sum II	Medium	62.6%	Backtracking Binary Tree+2	Read
114. Flatten Binary Tree to Linked List	Medium	71.0%	Binary Tree Depth-First Search+3	Read
116. Populating Next Right Pointers in Each Node	Medium	67.6%	Binary Tree Breadth-First Search+3	Read
117. Populating Next Right Pointers in Each Node II	Medium	57.9%	Binary Tree Breadth-First Search+3	Read
120. Triangle	Medium	59.9%	Array Dynamic Programming	Read
122. Best Time to Buy and Sell Stock II	Medium	71.4%	Array Dynamic Programming+1	Read
128. Longest Consecutive Sequence	Medium	47.0%	Array Hash Table+1	Read
129. Sum Root to Leaf Numbers	Medium	70.3%	Binary Tree Depth-First Search+1	Read
130. Surrounded Regions	Medium	46.1%	Array Breadth-First Search+3	Read
131. Palindrome Partitioning	Medium	74.4%	Backtracking Dynamic Programming+1	Read
133. Clone Graph	Medium	66.1%	Breadth-First Search Depth-First Search+2	Read
134. Gas Station	Medium	48.4%	Array Greedy	Read
137. Single Number II	Medium	67.4%	Array Bit Manipulation	Read
138. Copy List with Random Pointer	Medium	63.2%	Hash Table Linked List	Read
139. Word Break	Medium	49.8%	Array Dynamic Programming+4	Read
142. Linked List Cycle II	Medium	58.7%	Hash Table Linked List+1	Read
143. Reorder List	Medium	66.0%	Linked List Recursion+2	Read
146. LRU Cache	Medium	47.6%	Design Doubly-Linked List+2	Read
147. Insertion Sort List	Medium	59.9%	Linked List Sorting	Read
148. Sort List	Medium	65.2%	Divide and Conquer Linked List+3	Read
150. Evaluate Reverse Polish Notation	Medium	58.5%	Array Math+1	Read
151. Reverse Words in a String	Medium	57.8%	String Two Pointers	Read
152. Maximum Product Subarray	Medium	36.7%	Array Dynamic Programming	Read
153. Find Minimum in Rotated Sorted Array	Medium	55.3%	Array Binary Search	Read
155. Min Stack	Medium	58.5%	Design Stack	Read
156. Binary Tree Upside Down	Medium	65.4%	Binary Tree Depth-First Search+1	Read
159. Longest Substring with At Most Two Distinct Characters	Medium	57.0%	Hash Table Sliding Window+1	Read
161. One Edit Distance	Medium	34.4%	String Two Pointers	Read
162. Find Peak Element	Medium	46.8%	Array Binary Search	Read
164. Maximum Gap	Medium	52.8%	Array Bucket Sort+2	Read
165. Compare Version Numbers	Medium	46.8%	String Two Pointers	Read
166. Fraction to Recurring Decimal	Medium	31.3%	Hash Table Math+1	Read

#82Medium

Remove Duplicates from Sorted List II

Linked ListTwo Pointers

Acceptance: 52.2%

#86Medium

Partition List

Linked ListTwo Pointers

Acceptance: 62.0%

#89Medium

Gray Code

BacktrackingBit ManipulationMath

Acceptance: 65.6%

#90Medium

Subsets II

ArrayBacktrackingBit Manipulation

Acceptance: 61.7%

#91Medium

Decode Ways

Dynamic ProgrammingString

Acceptance: 38.3%

#92Medium

Reverse Linked List II

Linked List

Acceptance: 52.4%

#93Medium

Restore IP Addresses

BacktrackingString

Acceptance: 56.7%

#95Medium

Unique Binary Search Trees II

BacktrackingBinary Search TreeBinary Tree+2

Acceptance: 63.3%

#96Medium

Unique Binary Search Trees

Binary Search TreeBinary TreeDynamic Programming+2

Acceptance: 64.0%

#97Medium

Interleaving String

Dynamic ProgrammingString

Acceptance: 44.4%

#98Medium

Validate Binary Search Tree

Binary Search TreeBinary TreeDepth-First Search+1

Acceptance: 36.1%

#99Medium

Recover Binary Search Tree

Binary Search TreeBinary TreeDepth-First Search+1

Acceptance: 60.9%

#102Medium

Binary Tree Level Order Traversal

Binary TreeBreadth-First SearchTree

Acceptance: 73.5%

#103Medium

Binary Tree Zigzag Level Order Traversal

Binary TreeBreadth-First SearchTree

Acceptance: 64.4%

#105Medium

Construct Binary Tree from Preorder and Inorder Traversal

ArrayBinary TreeDivide and Conquer+2

Acceptance: 69.1%

#106Medium

Construct Binary Tree from Inorder and Postorder Traversal

ArrayBinary TreeDivide and Conquer+2

Acceptance: 69.4%

#107Medium

Binary Tree Level Order Traversal II

Binary TreeBreadth-First SearchTree

Acceptance: 69.0%

#109Medium

Convert Sorted List to Binary Search Tree

Binary Search TreeBinary TreeDivide and Conquer+2

Acceptance: 67.4%

#113Medium

Path Sum II

BacktrackingBinary TreeDepth-First Search+1

Acceptance: 62.6%

#114Medium

Flatten Binary Tree to Linked List

Binary TreeDepth-First SearchLinked List+2

Acceptance: 71.0%

#116Medium

Populating Next Right Pointers in Each Node

Binary TreeBreadth-First SearchDepth-First Search+2

Acceptance: 67.6%

#117Medium

Populating Next Right Pointers in Each Node II

Binary TreeBreadth-First SearchDepth-First Search+2

Acceptance: 57.9%

#120Medium

Triangle

ArrayDynamic Programming

Acceptance: 59.9%

#122Medium

Best Time to Buy and Sell Stock II

ArrayDynamic ProgrammingGreedy

Acceptance: 71.4%

#128Medium

Longest Consecutive Sequence

ArrayHash TableUnion Find

Acceptance: 47.0%

#129Medium

Sum Root to Leaf Numbers

Binary TreeDepth-First SearchTree

Acceptance: 70.3%

#130Medium

Surrounded Regions

ArrayBreadth-First SearchDepth-First Search+2

Acceptance: 46.1%

#131Medium

Palindrome Partitioning

BacktrackingDynamic ProgrammingString

Acceptance: 74.4%

#133Medium

Clone Graph

Breadth-First SearchDepth-First SearchGraph+1

Acceptance: 66.1%

#134Medium

Gas Station

ArrayGreedy

Acceptance: 48.4%

#137Medium

Single Number II

ArrayBit Manipulation

Acceptance: 67.4%

#138Medium

Copy List with Random Pointer

Hash TableLinked List

Acceptance: 63.2%

#139Medium

Word Break

ArrayDynamic ProgrammingHash Table+3

Acceptance: 49.8%

#142Medium

Linked List Cycle II

Hash TableLinked ListTwo Pointers

Acceptance: 58.7%

#143Medium

Reorder List

Linked ListRecursionStack+1

Acceptance: 66.0%

#146Medium

LRU Cache

DesignDoubly-Linked ListHash Table+1

Acceptance: 47.6%

#147Medium

Insertion Sort List

Linked ListSorting

Acceptance: 59.9%

#148Medium

Sort List

Divide and ConquerLinked ListMerge Sort+2

Acceptance: 65.2%

#150Medium

Evaluate Reverse Polish Notation

ArrayMathStack

Acceptance: 58.5%

#151Medium

Reverse Words in a String

StringTwo Pointers

Acceptance: 57.8%

#152Medium

Maximum Product Subarray

ArrayDynamic Programming

Acceptance: 36.7%

#153Medium

Find Minimum in Rotated Sorted Array

ArrayBinary Search

Acceptance: 55.3%

#155Medium

Min Stack

DesignStack

Acceptance: 58.5%

#156Medium

Binary Tree Upside Down

Binary TreeDepth-First SearchTree

Acceptance: 65.4%

#159Medium

Longest Substring with At Most Two Distinct Characters

Hash TableSliding WindowString

Acceptance: 57.0%

#161Medium

One Edit Distance

StringTwo Pointers

Acceptance: 34.4%

#162Medium

Find Peak Element

ArrayBinary Search

Acceptance: 46.8%

#164Medium

Maximum Gap

ArrayBucket SortRadix Sort+1

Acceptance: 52.8%

#165Medium

Compare Version Numbers

StringTwo Pointers

Acceptance: 46.8%

#166Medium

Fraction to Recurring Decimal

Hash TableMathString

Acceptance: 31.3%

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