98. Validate Binary Search Tree

https://leetcode.com/problems/validate-binary-search-tree/

JavaScript

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

function isValid(root, min, max) {
  if (!root) {
    return true
  }

  if (root.val <= min || root.val >= max) {
    return false
  }

  return isValid(root.left, min, root.val) && isValid(root.right, root.val, max)
}

Python

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None


class Solution(object):

    def isValidBST(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        return self.isValid(root, -float('inf'), float('inf'))

    def isValid(self, root, low, high):
        if not root:
            return True
        if root.val <= low or root.val >= high:
            return False
        return self.isValid(root.left, low, root.val) and self.isValid(root.right, root.val, high)

Go

import "math"

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func isValidBST(root *TreeNode) bool {
	return isValid(root, math.MinInt64, math.MaxInt64)
}

func isValid(root *TreeNode, min int, max int) bool {
	if root == nil {
		return true
	}
	if root.Val <= min || root.Val >= max {
		return false
	}
	return isValid(root.Left, min, root.Val) && isValid(root.Right, root.Val, max)
}