[LeetCode98] Validate Binary Search Tree

题目:

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.

 

Example 1:

    2
   / \
  1   3

Binary tree [2,1,3], return true.

 

Example 2:

    1
   / \
  2   3

Binary tree [1,2,3], return false.

分类:Tree DFS

代码:

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     bool isValidBST(TreeNode* root) {
13       return helper(root,LONG_MIN,LONG_MAX);
14     }
15     
16     bool helper(TreeNode* root, long min, long max)
17     {
18         if(!root)
19             return true;
20         if(root->val <= min || root->val >= max)
21             return false;
22         return helper(root->left,min,root->val) && helper(root->right,root->val,max);
23     }
24 };

 

posted @ 2016-08-16 11:48  zhangbaochong  阅读(237)  评论(0编辑  收藏  举报