| 标题 | Validate Binary Search Tree |
| 通过率 | 21.9% |
| 难度 | 中等 |
Given a binary tree, determine if it is a valid binary search tree (BST).
Assume a BST is defined as follows:
confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.
本题就是确定一棵树是否为二叉排序树，左<中<右，可以用中序遍历去判断，也可以用一个范围值去判断当前节点是否在其中，范围的下界是左边的树，范围的右界是右边的树，直接看代码了：
1 /** 2 * Definition for binary tree 3 * public class TreeNode { 4 * int val; 5 * TreeNode left; 6 * TreeNode right; 7 * TreeNode(int x) { val = x; } 8 * } 9 */ 10 public class Solution { 11 public boolean isValidBST(TreeNode root) { 12 return isBst(root,Long.MIN_VALUE,Long.MAX_VALUE); 13 } 14 public boolean isBst(TreeNode root,long min,long max){ 15 if(root==null) return true; 16 if(root.val<=min||root.val>=max)return false; 17 return isBst(root.left,min,root.val)&&isBst(root.right,root.val,max); 18 19 } 20 }
leetcode------Validate Binary Search Tree
原文：http://www.cnblogs.com/pkuYang/p/4299366.html