LeetCode OJ：Validate Binary Search Tree（合法的二叉搜索树）

 1 class Solution {
 2 public:
 3     bool isValidBST(TreeNode* root) {
 4        return checkValid(root, INT_MIN, INT_MAX);
 5     }
 6 
 7     bool checkValid(TreeNode * root, int left, int right)
 8     {
 9         if(root == NULL)
10             return true;
11         return(root->val > left && root->val < right && checkValid(root->left, left, root->val) ]
12             && checkValid(root->right, root->val, right));
13     }
14 };

 1 class Solution {
 2 public:
 3     bool isValidBST(TreeNode* root) {
 4         inOrder(root);
 5         int sz = res.size();
 6         if(sz < 2) return true;
 7         for(int i = 1; i < sz; ++i){
 8             if(res[i] <= res[i - 1])
 9                 return false;
10         }
11         return true;
12     }
13 
14     void inOrder(TreeNode * root)
15     {
16         if(!root) return;
17         if(root->left) inOrder(root->left);
18         res.push_back(root->val);
19         if(root->right) inOrder(root->right);
20     }
21 private:
22     vector<int> res;
23 };