LeetCode 98 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:

1 The left subtree of a node contains only nodes with keys less than the node's key.
2 The right subtree of a node contains only nodes with keys greater than the node's key.
3 Both the left and right subtrees must also be binary search trees.

要理解bst的以上3点性质，一般bst的遍历，都需要保存一个interval，保证该bst子树的所有node的值都在interval范围内！！！

代码：

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean isValidBST(TreeNode root) {
        return isValidRecursive(root, Long.MIN_VALUE, Long.MAX_VALUE);
    }
    
    public boolean isValidRecursive(TreeNode root, long min, long max) {
        return root == null ||
        root.val < max && root.val > min && 
        isValidRecursive(root.left, min, root.val) && isValidRecursive(root.right, root.val, max);
    }
    
}