leetcode@ [124] Binary Tree Maximum Path Sum (DFS)

/**
 * 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 {
public:
    int res = INT_MIN;
    
    int dfs(TreeNode* root) {
        if(!root) return 0;
        
        int l = dfs(root->left);
        int r = dfs(root->right);
        
        int rhs = root->val;
        if(l > 0) rhs += l;
        if(r > 0) rhs += r;
        res = max(res, rhs);
        
        return max(l, r) <= 0? root->val: max(l, r) + root->val; 
    }
    
    int maxPathSum(TreeNode* root) {
        if(!root) return 0;
        
        dfs(root);
        
        return res;
    }
};