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:

/**
 * 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) {
        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<min || root.val>max)
            return false;
        boolean solution = isValidBST(root.left, min, root.val-1);
        solution = solution && isValidBST(root.right, root.val+1, max);
        return solution;
    }
}