/************************************************************************/

        /*       38:      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.

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

         *

         * */

        

        

        /*

         * 二叉搜索树：

         *

         * */

        

        /**

         * Definition for binary tree

         * public class TreeNode {

         *     int val;

         *     TreeNode left;

         *     TreeNode right;

         *     TreeNode(int x) { val = x; }

         * }

         */

        

/**1 : max(left nodes) < root&& min(right nodes)>root *******************************************/

// 当 min(left node )>root || max(right nodes)<root 时 就肯定不是了

 

public boolean isValidBST(TreeNode root)        {            return  validate(root,null,null);        }        boolean validate(TreeNode node, TreeNode tmin, TreeNode tmax) {            if (node == null) return true;            if (tmin != null && node.val <= tmin.val) return false;            if (tmax != null && node.val >= tmax.val) return false;            return validate(node.left, tmin, node) && validate(node.right, node, tmax);        }