[Leetcode 124, Hard] Binary Tree Maximum Path Sum

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Problem:

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.

Analysis:

The solution comes from the website: http://fisherlei.blogspot.com/2013/01/leetcode-binary-tree-maximum-path-sum.html

Solutioins:

C++:

    int maxPathSum(TreeNode* root)     {        int maxAcrossRoot = INT_MIN;          int maxEndByRoot = GetMax(root, maxAcrossRoot);          return std::max(maxAcrossRoot, maxEndByRoot);      }        int GetMax(TreeNode *node, int& maxAcrossRoot)      {          if(node == NULL) return 0;          int left = GetMax(node->left, maxAcrossRoot);          int right = GetMax(node->right, maxAcrossRoot);          int cMax = node->val;          if(left>0)              cMax += left;          if(right>0)              cMax += right;          maxAcrossRoot = std::max(maxAcrossRoot, cMax);          return std::max(node->val, std::max(node->val + left, node->val + right));      }

Java:

Python:

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