[LeetCode] Validate Binary Search Tree

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

Assume a 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.

[Solution].java

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean isValidBST(TreeNode root) {
        // Start typing your Java solution below
        // DO NOT write main() function
        return isValidBST(root, Integer.MIN_VALUE, Integer.MAX_VALUE);
    }

    public boolean isValidBST(TreeNode root, int min, int max){
        if(root == null) return true;
        if(root.val >= max || root.val <= min) return false;
        return isValidBST(root.left, min, root.val) && isValidBST(root.right, root.val, max);
    }
}