[Leetcode] 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.

后序遍历！

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int myMax(int a, int b, int c) {
        a = a > b ? a : b;
        return a > c ? a : c;
    }
    
    int getMaxSum(TreeNode *root, int &max_sum) {
        if (root == NULL) {
            return 0;
        }
        int local_max = root->val;
        int left = getMaxSum(root->left, max_sum);
        int right = getMaxSum(root->right, max_sum);
        local_max += (left > 0) ? left : 0;
        local_max += (right > 0) ? right : 0;
        max_sum = max_sum > local_max ? max_sum : local_max;
        return myMax(root->val, root->val + left, root->val + right);
    }
    
    int maxPathSum(TreeNode *root) {
        int max_sum = INT_MIN;
        getMaxSum(root, max_sum);
        return max_sum;
    }
};