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 less than the node's key.
- The right subtree of a node contains only nodes with keys 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.
Constraints
- The number of nodes in the tree is in the range
[1, 104]. -2<sup>31</sup> <= Node.val <= 2<sup>31</sup> - 1
Related Topics
- Tree
- Depth-First Search
- Binary Tree
- Binary Search Tree
Recursively check if each left tree is less than root and each right tree is greater than root, define the min and max to check the minimum and maximum parent value.