leetcode 98. 验证二叉搜索树

题目如下

数据范围

通过代码

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    long long t = INT_MIN;
    bool ans = true;
    void in(TreeNode *root){
        if(root == nullptr || !ans)return;
        in(root->left);
        if(root->val <= t){
            ans = false;
            return;
        }
        t = root->val;
        in(root->right);
    }
    bool isValidBST(TreeNode* root) {
        t = t * 2;
        in(root);
        return ans;
    }
};