[LeetCode-124] Binary Tree Maximum Path Sum

Binary Tree Maximum Path Sum

Given a binary tree, find the maximum path sum.

The path may start and end at any node in the tree.

For example:
Given the below binary tree,

       1
      / \
     2   3

 

Return 6.

 

二叉树后序历遍的变形。

 

 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 result;
13     inline bool has_left(TreeNode *root) {
14         return NULL != root->left;
15     }
16     inline bool has_right(TreeNode *root) {
17         return NULL != root->right;
18     }
19     void trace_last(TreeNode *pnode) {
20         int tmpv = pnode->val, tmplv = pnode->val, tmprv = pnode->val, tmpresult = -INT_MAX;
21         if (has_left(pnode)) {
22             trace_last(pnode->left);
23             tmplv = max<int>(tmpv, pnode->val + pnode->left->val);
24         }
25         if (has_right(pnode)) {
26             trace_last(pnode->right);
27             tmprv = max<int>(tmpv, pnode->val + pnode->right->val);
28         }
29         tmpresult = max<int>(max<int>(tmpv, tmplv + tmprv - tmpv), max<int>(tmplv, tmprv));
30         if (tmpresult > result) {
31             result = tmpresult;
32         }
33         pnode->val = max<int>(max<int>(tmplv, tmprv), tmpv);
34     }
35     int maxPathSum(TreeNode *root) {
36         // Start typing your C/C++ solution below
37         // DO NOT write int main() function
38         result = -INT_MAX;
39         trace_last(root);
40         return result;
41     }
42 };
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posted on 2013-08-29 10:06  似溦若岚  阅读(179)  评论(0)    收藏  举报

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