124. Binary Tree Maximum Path Sum

题目

Given a binary tree, find the maximum path sum.

For this problem, a path is defined as any sequence of nodes from some starting node to any node in the tree along the parent-child connections. The path must contain at least one node and does not need to go through the root.

For example:

Given the below binary tree,
       1
      / \
     2   3

Return 6.

解题思路

见程序注释