Binary Search Trees Recommended Order By Topic Binary Tree Traversals Order Question Difficulty Votes 1 Binary Tree Inorder Traversal Easy 2 Binary Tree Preorder Traversal Easy 3 Binary Tree Postorder Traversal Easy 4 Convert Sorted Array to Binary Tree Easy 5 Binary Tree Level Order Traversal Medium 6 Binary Tree Zigzag Level Order Traversal Medium 7 Construct Binary Tree from Preorder and Inorder Traversal Medium 8 Serialize and Deserialize Binary Tree Hard Binary Tree Operations Order Question Difficulty Votes 1 Maximum Depth of Binary Tree Easy 2 Same Tree Easy 3 Subtree of Another Tree Easy 4 Invert Binary Tree Easy 5 Path Sum Easy 6 Validate Binary Search Tree Medium 7 Symmmetric Tree Medium 8 K-th Smallest Element in a BST Medium 9 Flatten Binary Tree to Linked List Medium 10 Binary Tree Maximum Path Sum Hard