110. Balanced Binary Tree | solution | easy, bfs, trees |

102. Binary Tree Level Order Traversal | solution | Medium, bfs, trees |

107. Binary Tree Level Order Traversal II | solution | easy, bfs, trees |

101. Symmetric Tree | solution | easy, dfs, trees |

103. Binary Tree Zigzag Level Order Traversal | solution | Medium, bfs, trees |

199. Binary Tree Right Side View | solution | Medium, bfs, trees |

111. Minimum Depth of Binary Tree | solution | Easy, dfs, trees |

112. Path Sum | solution | Easy, bfs, trees |

113. Path Sum II | solution | Medium, bfs, backtrack, trees |

114. Flatten Binary Tree to Linked List | solution | Medium, bfs, trees |

100. Same Tree | solution | Easy, trees, bfs |

110. Balanced Binary Tree | solution | easy, tree, dfs |

1. Two Sum | solution | Easy, HashTable |

136. Single Number | solution | Easy, HashTable |

202. Happy Number | solution | Easy, Math, HashTable |

217. Contains Duplicate | solution | Easy, HashTable, Sets |

219. Contains Duplicate II | solution | Easy, HashTable |

1207. Unique Number of Occurrences | solution | Easy, HashTable |

13. Roman to Integer | solution | Easy, Strings |

151. Reverse Words in a String | solution | Medium, Strings |

14. Longest Common Prefix | solution | Easy, Strings |

67. Add Binary | solution | Easy, Strings |

22. Generate Parentheses | solution | Medium, Backtrack, Strings |

53. Maximum Subarray | solution | Easy, Dynamic Programming |

121. Best Time to Buy and Sell Stock | solution | Easy, Dynamic Programming |

122. Best Time to Buy and Sell Stock II | solution | Easy, Dynamic Programming |

62. Unique Paths | solution | Medium, Dynamic Programming |

120. Triangle | solution | Medium, Dynamic Programming |

49. Group Anagrams | solution | Medium, HashTable |

283. Move Zeroes | solution | Easy, Array |

844. Backspace String Compare | solution | Easy, String, Stack |

155. Min Stack | solution | Easy, Array, Stack |

543. Diameter of Binary Tree | solution | Easy, Trees, DFS |

5. Longest Palindromic Substring | solution | Medium, Strings |

144. Binary Tree Preorder Traversal | solution | Medium, dfs, trees |

94. Binary Tree Inorder Traversal | solution | Medium, dfs, trees |

739. Daily Temperatures | solution | Medium, Stack, Arrays |

3. Longest Substring Without Repeating Characters | solution | Medium, String, Arrays |

2. Add Two Numbers | solution | Medium, LinkedList |

300. Longest Increasing Subsequence | solution | Medium, Dynamic Programming |

46. Permutations | solution | Medium, Backtracking |

230. Kth Smallest Element in a BST | solution | Medium, Binary Search Tree, dfs |

56. Merge Intervals | solution | Medium, Arrays |

133. Clone Graph | solution | Medium, Graph |

841. Keys and Rooms | solution | Medium, Graph |