Day30: [LeetCode中等] 98. 驗證二叉搜索樹

Day30: [LeetCode中等] 98. 驗證二叉搜索樹

題源：

來自leetcode題庫：

https://leetcode-cn.com/problems/validate-binary-search-tree/

代碼：

dirty code湊合看吧

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    /*bool f(TreeNode* root){
        if(root->left==NULL&&root->right==NULL) return true;
        else if(root->left==NULL) return root->val<root->right->val;
        else if(root->right==NULL) return root->val>root->left->val;
        return root->val<root->right->val&&root->val>root->left->val&&f(root->left)&&f(root->right);
    }*/
    vector<int> res;
    void F(TreeNode* root){
        if(root){
            F(root->left);
            res.push_back(root->val);
            F(root->right);
        }
    }
    bool isValidBST(TreeNode* root) {
        if(!root) return true;
        F(root);
        for(int i=0;i<res.size()-1;i++){
            if(res[i]>=res[i+1]) return false;
        }
        return true;
    }
};