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
101. Symmetric Tree	Easy	61.5%	Binary Tree Breadth-First Search+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
104. Maximum Depth of Binary Tree	Easy	78.6%	Binary Tree Breadth-First Search+2	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
108. Convert Sorted Array to Binary Search Tree	Easy	75.9%	Array Binary Search Tree+3	Read
109. Convert Sorted List to Binary Search Tree	Medium	67.4%	Binary Search Tree Binary Tree+3	Read
110. Balanced Binary Tree	Easy	59.2%	Binary Tree Depth-First Search+1	Read
111. Minimum Depth of Binary Tree	Easy	53.7%	Binary Tree Breadth-First Search+2	Read
112. Path Sum	Easy	55.2%	Binary Tree Breadth-First Search+2	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
115. Distinct Subsequences	Hard	54.1%	Dynamic Programming String	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
118. Pascal's Triangle	Easy	79.4%	Array Dynamic Programming	Read
119. Pascal's Triangle II	Easy	67.8%	Array Dynamic Programming	Read
120. Triangle	Medium	59.9%	Array Dynamic Programming	Read
121. Best Time to Buy and Sell Stock	Easy	57.1%	Array Dynamic Programming	Read
122. Best Time to Buy and Sell Stock II	Medium	71.4%	Array Dynamic Programming+1	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
125. Valid Palindrome	Easy	54.2%	String Two Pointers	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
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
132. Palindrome Partitioning II	Hard	37.9%	Dynamic Programming String	Read
133. Clone Graph	Medium	66.1%	Breadth-First Search Depth-First Search+2	Read
134. Gas Station	Medium	48.4%	Array Greedy	Read
135. Candy	Hard	49.3%	Array Greedy	Read
136. Single Number	Easy	78.1%	Array Bit Manipulation	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
140. Word Break II	Hard	55.8%	Array Backtracking+5	Read
141. Linked List Cycle	Easy	54.6%	Hash Table Linked List+1	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
144. Binary Tree Preorder Traversal	Easy	76.6%	Binary Tree Depth-First Search+2	Read
145. Binary Tree Postorder Traversal	Easy	79.0%	Binary Tree Depth-First Search+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
149. Max Points on a Line	Hard	31.0%	Array Geometry+2	Read
150. Evaluate Reverse Polish Notation	Medium	58.5%	Array Math+1	Read

#101Easy

Symmetric Tree

Binary TreeBreadth-First SearchDepth-First Search+1

Acceptance: 61.5%

#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%

#104Easy

Maximum Depth of Binary Tree

Binary TreeBreadth-First SearchDepth-First Search+1

Acceptance: 78.6%

#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%

#108Easy

Convert Sorted Array to Binary Search Tree

ArrayBinary Search TreeBinary Tree+2

Acceptance: 75.9%

#109Medium

Convert Sorted List to Binary Search Tree

Binary Search TreeBinary TreeDivide and Conquer+2

Acceptance: 67.4%

#110Easy

Balanced Binary Tree

Binary TreeDepth-First SearchTree

Acceptance: 59.2%

#111Easy

Minimum Depth of Binary Tree

Binary TreeBreadth-First SearchDepth-First Search+1

Acceptance: 53.7%

#112Easy

Path Sum

Binary TreeBreadth-First SearchDepth-First Search+1

Acceptance: 55.2%

#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%

#115Hard

Distinct Subsequences

Dynamic ProgrammingString

Acceptance: 54.1%

#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%

#118Easy

Pascal's Triangle

ArrayDynamic Programming

Acceptance: 79.4%

#119Easy

Pascal's Triangle II

ArrayDynamic Programming

Acceptance: 67.8%

#120Medium

Triangle

ArrayDynamic Programming

Acceptance: 59.9%

#121Easy

Best Time to Buy and Sell Stock

ArrayDynamic Programming

Acceptance: 57.1%

#122Medium

Best Time to Buy and Sell Stock II

ArrayDynamic ProgrammingGreedy

Acceptance: 71.4%

#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%

#125Easy

Valid Palindrome

StringTwo Pointers

Acceptance: 54.2%

#126Hard

Word Ladder II

BacktrackingBreadth-First SearchHash Table+1

Acceptance: 27.7%

#127Hard

Word Ladder

Breadth-First SearchHash TableString

Acceptance: 46.3%

#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%

#132Hard

Palindrome Partitioning II

Dynamic ProgrammingString

Acceptance: 37.9%

#133Medium

Clone Graph

Breadth-First SearchDepth-First SearchGraph+1

Acceptance: 66.1%

#134Medium

Gas Station

ArrayGreedy

Acceptance: 48.4%

#135Hard

Candy

ArrayGreedy

Acceptance: 49.3%

#136Easy

Single Number

ArrayBit Manipulation

Acceptance: 78.1%

#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%

#140Hard

Word Break II

ArrayBacktrackingDynamic Programming+4

Acceptance: 55.8%

#141Easy

Linked List Cycle

Hash TableLinked ListTwo Pointers

Acceptance: 54.6%

#142Medium

Linked List Cycle II

Hash TableLinked ListTwo Pointers

Acceptance: 58.7%

#143Medium

Reorder List

Linked ListRecursionStack+1

Acceptance: 66.0%

#144Easy

Binary Tree Preorder Traversal

Binary TreeDepth-First SearchStack+1

Acceptance: 76.6%

#145Easy

Binary Tree Postorder Traversal

Binary TreeDepth-First SearchStack+1

Acceptance: 79.0%

#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%

#149Hard

Max Points on a Line

ArrayGeometryHash Table+1

Acceptance: 31.0%

#150Medium

Evaluate Reverse Polish Notation

ArrayMathStack

Acceptance: 58.5%

1 2 3 479 80 81

Page 3 of 81

Master DSA with Step-by-Step Solutions

Each solution article on FleetCode breaks down the problem into multiple approaches, from brute force to optimal, with detailed explanations and code in Python, Java, C++ and more. Understanding why an approach works - not just copying code - is what separates candidates who clear interviews from those who don't.

How to Use These Solutions

Try the problem first: Spend at least 20 minutes before reading the solution
Read all approaches: Start from brute force to understand the problem fully, then study the optimized solution
Understand the complexity: Pay attention to time and space analysis for each approach
Code it yourself: After understanding the approach, close the solution and implement from memory
Revisit after a week: Spaced repetition helps retain problem-solving patterns