LeetCode——Validate Binary Search Tree

最新推荐文章于 2025-07-29 19:45:28 发布

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本文介绍了一种简单有效的方法来判断给定的二叉树是否为有效的二叉搜索树（BST）。通过中序遍历的方式获取节点值，并检查其是否构成递增序列来实现验证。

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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.

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

» Solve this problem

我用了一个没有技术含量的方法，把树中序遍历，然后看是否为递增序列。

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
 
class Solution {
private:
    vector<int> vals;
    
    void traverse(TreeNode *root) {
        if (root != NULL) {
            traverse(root->left);
            vals.push_back(root->val);
            traverse(root->right);
        }    
    }
    
public:
    bool isValidBST(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vals.clear();
        traverse(root);
        for (int i = 1; i < vals.size(); i++) {
            if (vals[i] <= vals[i - 1]) {
                return false;
            }
        }
        return true;
    }
};