Validate BST

is-valid-bst.js

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} node
 * @return {boolean}
 */
const isValidBST = (node) =>
    validateNode(node, -Infinity, Infinity);

const validateNode = (node, min, max) => {
    if (node == null) return true;
    if (node.val <= min || node.val >= max) {
        return false;
    }
    
    return validateNode(node.left, min, node.val) && validateNode(node.right, node.val, max);
}