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

/**
 * 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 maxSum(TreeNode * root, int & globe_max){  
        if(!root) {  
            return 0;  
        }  
        int local_max = root->val;  
        int left = maxSum(root->left, globe_max);  
        int right = maxSum(root->right, globe_max);  
        local_max = max(local_max, local_max+left);
        local_max = max(local_max, local_max+right);
        globe_max = max(globe_max, local_max);  
        return max(root->val, max(root->val+right, root->val+left) );  
    }  
    int maxPathSum(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int globe_max = root->val;  
        int maxVal = maxSum(root, globe_max);  
        return max(globe_max, maxVal);  
    }
};

 C#:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int maxSum(TreeNode root, ref int globeMax)
    {
        if (root == null) return 0;
        int localMax = root.val;
        int left = maxSum(root.left, ref globeMax);
        int right = maxSum(root.right, ref globeMax);
        localMax = Math.Max(localMax, localMax + left);
        localMax = Math.Max(localMax, localMax + right);
        globeMax = Math.Max(globeMax, localMax);
        return Math.Max(root.val, Math.Max(root.val + left, root.val + right));
    }
    public int MaxPathSum(TreeNode root) {
        int globeMax = root.val;
        int maxVal = maxSum(root, ref globeMax);
        return Math.Max(globeMax, maxVal);
    }
}