98. 验证二叉搜索树 – Blog of Aspirer

题目链接：https://leetcode.cn/problems/validate-binary-search-tree/

没能把中序遍历和搜索二叉树联系起来，看的评论区题解。

/**
 * 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  pre = (long long)INT_MIN - 1;
    bool middle_first(TreeNode* root) {
        if (!root) {
            return true;
        }
        bool l, r;
        l = middle_first(root->left);
        
        if (pre >= root->val) {
            return false;
        }
        pre = root->val;
        cout << root->val << ", ";
        r = middle_first(root->right);

        return l & r;
    }

    bool isValidBST(TreeNode* root) {
        if (!root) {
            return true;
        }
        return middle_first(root);

    }
};

/**

* 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 pre = (long long)INT_MIN - 1;

bool middle_first(TreeNode* root) {

if (!root) {

return true;

}

bool l, r;

l = middle_first(root->left);

if (pre >= root->val) {

return false;

}

pre = root->val;

cout << root->val << ", ";

r = middle_first(root->right);

return l & r;

}

bool isValidBST(TreeNode* root) {

if (!root) {

return true;

}

return middle_first(root);

}

};