101 
Symmetric Tree 
Easy 
Tree

Depthfirst Search

Breadthfirst Search

102 
Binary Tree Level Order Traversal 
Medium 
Tree

Breadthfirst Search

103 
Binary Tree Zigzag Level Order Traversal 
Medium 
Stack 
Tree

Breadthfirst Search

104 
Maximum Depth of Binary Tree 
Easy 
Tree

Depthfirst Search

105 
Construct Binary Tree from Preorder and Inorder Traversal 
Medium 
Array

Tree

Depthfirst Search

106 
Construct Binary Tree from Inorder and Postorder Traversal 
Medium 
Array

Tree

Depthfirst Search

107 
Binary Tree Level Order Traversal II 
Medium 
Tree

Breadthfirst Search

108 
Convert Sorted Array to Binary Search Tree 
Easy 
Tree

Depthfirst Search

110 
Balanced Binary Tree 
Easy 
Tree

Depthfirst Search

111 
Minimum Depth of Binary Tree 
Easy 
Tree

Depthfirst Search Breadthfirst Search

112 
Path Sum 
Easy 
Tree

Depthfirst Search

113 
Path Sum II 
Medium 
Tree

Depthfirst Search

114 
Flatten Binary Tree to Linked List 
Medium 
Tree

Depthfirst Search

116 
Populating Next Right Pointers in Each Node 
Medium 
Tree

Depthfirst Search

117 
Populating Next Right Pointers in Each Node II 
Medium 
Tree

Depthfirst Search

118 
Pascal's Triangle 
Easy 
Array

119 
Pascal's Triangle II 
Easy 
Array

120 
Triangle 
Medium 
Array

Dynamic Programming

121 
Best Time to Buy and Sell Stock 
Easy 
Array

Dynamic Programming

122 
Best Time to Buy and Sell Stock II 
Easy 
Array

Greedy

123 
Best Time to Buy and Sell Stock III 
Hard 
Array

Dynamic Programming

124 
Binary Tree Maximum Path Sum 
Hard 
Tree

Depthfirst Search

126 
Word Ladder II 
Hard 
Array

String

Backtracking 
Breadthfirst Search

129 
Sum Root to Leaf Numbers 
Medium 
Tree

Depthfirst Search

130 
Surrounded Regions 
Medium 
Depthfirst Search

Breadthfirst Search

Union Find

141 
Linked List Cycle 
Easy 

142 
Linked List Cycle II 
Medium 

143 
Reorder List 
Medium 

144 
Binary Tree Preorder Traversal 
Medium 
Stack 
Tree

145 
Binary Tree Postorder Traversal 
Medium 
Tree

Stack

146 
LRU Cache 
Medium 

147 
Insertion Sort List 
Medium 

148 
Sort List 
Medium 

149 
Max Points on a Line 
Hard 

150 
Evaluate Reverse Polish Notation 
Medium 

151 
Reverse Words in a String 
Medium 

152 
Maximum Product Subarray 
Medium 
Array

Dynamic Programming

153 
Find Minimum in Rotated Sorted Array 
Medium 

154 
Find Minimum in Rotated Sorted Array II 
Hard 

155 
Min Stack 
Easy 

156 
Binary Tree Upside Down 
Medium 
Tree

160 
Intersection of Two Linked Lists 
Easy 

162 
Find Peak Element 
Medium 

164 
Maximum Gap 
Hard 

165 
Compare Version Numbers 
Medium 

166 
Fraction to Recurring Decimal 
Medium 

167 
Two Sum II  Input array is sorted 
Easy 

168 
Excel Sheet Column Title 
Easy 

169 
Majority Element 
Easy 

171 
Excel Sheet Column Number 
Easy 

172 
Factorial Trailing Zeroes 
Easy 

173 
Binary Search Tree Iterator 
Medium 
Stack 
Tree

Design

174 
Dungeon Game 
Hard 

176 
Second Highest Salary 
Easy 

179 
Largest Number 
Medium 

188 
Best Time to Buy and Sell Stock IV 
Hard 

189 
Rotate Array 
Medium 

190 
Reverse Bits 
Easy 

191 
Number of 1 Bits 
Easy 

198 
House Robber 
Medium 

199 
Binary Tree Right Side View 
Medium 
Tree

Depthfirst Search

Breadthfirst Search

200 
Number of Islands 
Medium 
