leetcode------Validate Binary Search Tree

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:

  • 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.

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 }

 

posted @ 2015-02-25 11:46  pku_smile  阅读(132)  评论(0编辑  收藏  举报