LeetCode: Validate Binary Search Tree

看了别人的代码

 1 /**

 2  * Definition for binary tree

 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 public:

12     bool dfs(TreeNode *root, int MIN, int MAX) {

13         if (!root) return true;

14         if (root->val > MIN && root->val < MAX && dfs(root->left, MIN, root->val) && dfs(root->right, root->val, MAX))

15             return true;

16         else return false;

17     }

18     bool isValidBST(TreeNode *root) {

19         // Start typing your C/C++ solution below

20         // DO NOT write int main() function

21         return dfs(root, INT_MIN, INT_MAX);

22     }

23 };

 自己另外写了个，比较好懂

 1 /**

 2  * Definition for binary tree

 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 public:

12     void dfs(TreeNode *root, TreeNode * &pre, bool &flag) {

13         if (!root) return;

14         dfs(root->left, pre, flag);

15         if (pre && pre->val >= root->val) {

16             flag = false;

17             return;

18         }

19         pre = root;

20         dfs(root->right, pre, flag);

21     }

22     bool isValidBST(TreeNode *root) {

23         // Start typing your C/C++ solution below

24         // DO NOT write int main() function

25         TreeNode *pre = NULL;

26         bool flag = true;

27         dfs(root, pre, flag);

28         return flag;

29     }

30 };

 C#

 1 /**

 2  * Definition for a binary tree node.

 3  * public class TreeNode {

 4  *     public int val;

 5  *     public TreeNode left;

 6  *     public TreeNode right;

 7  *     public TreeNode(int x) { val = x; }

 8  * }

 9  */

10 public class Solution {

11     public bool IsValidBST(TreeNode root) {

12         return dfs(root, Int64.MinValue, Int64.MaxValue);

13     }

14     public bool dfs(TreeNode root, Int64 Min, Int64 Max) {

15         if (root == null) return true;

16         return root.val > Min && root.val < Max && dfs(root.left, Min, root.val) && dfs(root.right, root.val, Max);

17     }

18 }

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