/************************************************************************/
/* 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); }