Tree

1.Easy

(101)Symmetric Tree

(104)Maximum Depth of Binary Tree

(226)Invert Binary Tree

(543)Diameter of Binary Tree

(617)Merge Two Binary Trees

2.Medium

(94)Binary Tree Inorder Traversal

(96)Unique Binary Search Trees

(98)Validate Binary Search Tree

(102)Binary Tree Level Order Traversal

(105)Construct Binary Tree from Preorder and Inorder Traversal

(114)Flatten Binary Tree to Linked List

(337)House Robber III

(437)Path Sum III

(538)Convert BST to Greater Tree

3.Hard

(124)Binary Tree Maximum Path Sum

(297)Serialize and Deserialize Binary Tree