LeetCode:Validate Binary Search Tree

最新推荐文章于 2025-09-10 15:24:29 发布

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最新推荐文章于 2025-09-10 15:24:29 发布

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文章标签：数据结构与算法

原文链接：http://www.cnblogs.com/TenosDoIt/p/3448413.html

本文介绍了一种通过中序遍历来验证二叉树是否为有效的二叉搜索树的方法，并提供了一个C++实现示例。

题目链接

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.

分析：根据BST中序遍历序列有序的性质判断，只要在中序遍历二叉树的代码基础上加上判断相邻元素关系的语句即可本文地址

 1 /**
 2  * Definition for binary tree
 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         // IMPORTANT: Please reset any member data you declared, as
14         // the same Solution instance will be reused for each test case.
15         //注意题目要求是 less than和greater than;
16         stack<TreeNode*> S;
17         TreeNode *pre = NULL, *p = root;
18         while(p || S.empty() == false)
19         {
20             while(p)
21             {
22                 S.push(p);
23                 p = p->left;
24             }
25             if(S.empty() == false)
26             {
27                 p = S.top();
28                 S.pop();
29                 if(pre && p->val <= pre->val)return false;
30                 pre = p;
31                 p = p->right;
32             }
33         }
34         return true;
35     }
36 };