LeetCode 0124 - Binary Tree Maximum Path Sum

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
private:
    int res = INT_MIN;
    int getSonMax(TreeNode* cur) {
        if(cur == NULL)
            return 0;
        int l = max(0, getSonMax(cur->left));
        int r = max(0, getSonMax(cur->right));
        res = max(res, l + r + cur->val);
        return cur->val + max(l, r);
    }
public:
    int maxPathSum(TreeNode* root) {
        getSonMax(root);
        return res;
    }
};