LeetCode: Binary Tree Maximum Path Sum

这题比较难，没理顺关系，做了很多次还只是过了small judge，于是去看网上答案，然后再改了改，关键在于local_max和globe_max，globe_max要随时改得，而maxsum函数只是返回最大路径

 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     int maxSum(TreeNode * root, int & globe_max){  

13         if(!root) {  

14             return 0;  

15         }  

16         int local_max = root->val;  

17         int left = maxSum(root->left, globe_max);  

18         int right = maxSum(root->right, globe_max);  

19         local_max = max(local_max, local_max+left);

20         local_max = max(local_max, local_max+right);

21         globe_max = max(globe_max, local_max);  

22         return max(root->val, max(root->val+right, root->val+left) );  

23     }  

24     int maxPathSum(TreeNode *root) {

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

26         // DO NOT write int main() function

27         int globe_max = root->val;  

28         int maxVal = maxSum(root, globe_max);  

29         return max(globe_max, maxVal);  

30     }

31 };

 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 int maxSum(TreeNode root, ref int globeMax)

12     {

13         if (root == null) return 0;

14         int localMax = root.val;

15         int left = maxSum(root.left, ref globeMax);

16         int right = maxSum(root.right, ref globeMax);

17         localMax = Math.Max(localMax, localMax + left);

18         localMax = Math.Max(localMax, localMax + right);

19         globeMax = Math.Max(globeMax, localMax);

20         return Math.Max(root.val, Math.Max(root.val + left, root.val + right));

21     }

22     public int MaxPathSum(TreeNode root) {

23         int globeMax = root.val;

24         int maxVal = maxSum(root, ref globeMax);

25         return Math.Max(globeMax, maxVal);

26     }

27 }

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