124.cpp

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
    int ans;
    int max_val_node;
public:
    int _maxPathSum(TreeNode *root) {
        if (!root) {
            return 0;
        }

        max_val_node = max(max_val_node, root->val);

        int left = _maxPathSum(root->left);
        int right = _maxPathSum(root->right);

        if (left < 0) {
            left = 0;
        }
        if (right < 0) {
            right = 0;
        }

        ans = max(ans, max({
            left,
            right,
            left + right + root->val
        }));

        return max({
            left,
            right
        }) + root->val;
    }

    int maxPathSum(TreeNode* root) {
        ans = 0;
        max_val_node = INT_MIN;
        _maxPathSum(root);
        if (ans == 0) {
            return max_val_node;
        }
        return ans;
    }
};