Validate Binary Search Tree

01 · Question

Given the root of a binary tree, determine if it is a valid binary search tree (BST).

02 · Solution

Reference solution

1def isValidBST(root: Optional[TreeNode]) -> bool:
2    def dfs(node: Optional[TreeNode], lo: float, hi: float) -> bool:
3        if not node:
4            return True
5        if not (lo < node.val < hi):
6            return False
7        return dfs(node.left, lo, node.val) and dfs(node.right, node.val, hi)
8    
9    return dfs(root, float('-inf'), float('inf'))

Invert Binary Tree

Tree Size