98. 验证二叉搜索树 

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution 
11 {
12     vector<int> nums;
13     void slove(TreeNode* root)
14     {
15         if(root == NULL) return;
16         slove(root->left);
17         nums.push_back(root->val);
18         slove(root->right);
19     }
20 public:
21     bool isValidBST(TreeNode* root) 
22     {
23         if(root == NULL) return true;
24         slove(root);
25         int n = nums.size();
26         for(int i = 1;i < n;i ++) 
27         {
28             if(nums[i] <= nums[i - 1]) return false;
29         }
30         return true;
31     }
32 };

 

 1 class Solution 
 2 {
 3 public:
 4     bool isValidBST(TreeNode* root) 
 5     {
 6         return dfs(root,INT_MIN,INT_MAX);
 7     }
 8 
 9     bool dfs(TreeNode* root,long long minv,long long maxv)
10     {
11         if(!root) return true;
12         if(root->val < minv || root->val > maxv) return false;
13         
14         //[负无穷，x - 1]和[x + 1,正无穷]中寻找
15         return dfs(root->left,minv,root->val - 1ll) && dfs(root->right,root->val + 1ll,maxv);
16     }
17 };

 

posted @ 2020-03-23 15:52  Jinxiaobo0509  阅读(122)  评论(0)    收藏  举报