[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.
  

  ?

  /**
   * 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,Long.MIN_VALUE,Long.MAX_VALUE);
  	}
  	
  	private boolean isValidBST(TreeNode root,long min,long max){
  		if(root == null) return true;
  		return root.val>min&&root.val
      
       
  ?
       
  ?
       
  ?