leetcode validBST

package com.bupt.acm.leetcode;

public class ValidBinary {

    private class TreeNode{
        int val;
        TreeNode left;
        TreeNode right;
        TreeNode(int x){
            val=x;
        }
    }
    public boolean isValidBST(TreeNode root){
        if(root==null){
            return true;
        }
        return validBST(root,Integer.MIN_VALUE,Integer.MAX_VALUE);
    }
    private boolean validBST(TreeNode root, int min, int max) {
        // TODO Auto-generated method stub
        if(root==null){
            return true;
        }
        if(root.val>min&&root.val<max){
            return validBST(root.left,min,root.val)&&validBST(root.right, root.val, max);
        }else{
            return false;
        }
    }
    
}