98\. Validate Binary Search Tree
# 98. Validate Binary Search Tree (opens new window)
# Description
Difficulty: Medium
Related Topics: Tree (opens new window), Depth-First Search (opens new window), Binary Search Tree (opens new window), Binary Tree (opens new window)
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
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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.
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Constraints:
- The number of nodes in the tree is in the range [1, 104].
- -231 <= Node.val <= 231 - 1
# Solution
Language: JavaScript
/**
* Definition for a binary tree node.
* function TreeNode(val, left, right) {
* this.val = (val===undefined ? 0 : val)
* this.left = (left===undefined ? null : left)
* this.right = (right===undefined ? null : right)
* }
*/
/**
* @param {TreeNode} root
* @return {boolean}
*/
var isValidBST = function(root) {
return helper(root)
};
const helper = (node, min = Number.MIN_SAFE_INTEGER, max = Number.MAX_SFFE_INTEGER) => {
if (!node) return true;
if (node.val <= min || node.val >= max) return false;
return helper(node.left, min, node.val) && helper(node.right, node.val, max);
}
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