#98

Validate Binary Search Tree

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tree · depth-first search · binary search tree · binary tree

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Description

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

A valid BST is defined as follows:

 - The left subtree of a node contains only nodes with keys strictly less than the node's key.

 - The right subtree of a node contains only nodes with keys strictly greater than the node's key.

 - Both the left and right subtrees must also be binary search trees.

Example 1:

Input: root = [2,1,3]
Output: true

Example 2:

Input: root = [5,1,4,null,null,3,6]
Output: false
Explanation: The root node's value is 5 but its right child's value is 4.

Solution