Validate Binary Search Tree

最新推荐文章于 2024-10-14 16:31:29 发布

a83610312

最新推荐文章于 2024-10-14 16:31:29 发布

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本文链接：https://blog.youkuaiyun.com/a83610312/article/details/8910570

本文介绍如何通过中序遍历的方式验证给定的二叉树是否为有效的二叉搜索树（BST）。通过比较中序遍历过程中的每个节点与前一个节点的值，可以判断BST的性质。

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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.

比较简单，中序遍历，并保持上一个被遍历的值与当前值比较就行了。

代码如下：

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isValidBST(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
       if ( !root )
            return true;
        pre=-1000000;
        return check(root);
    }
    bool check(TreeNode* root)
    {
        if ( !root )
            return true;
        if ( check(root->left) )
        {
            if ( root->val <= pre)
                return false;
            pre=root->val;
            return check(root->right);
        }
        else
            return false;
            
    }
    int pre;
};