Leetcode-Solutions/124. Binary Tree Maximum Path Sum.cpp at main · amanhex/Leetcode-Solutions · GitHub

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/*
A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them.
A node can only appear in the sequence at most once. Note that the path does not need to pass through the root.
The path sum of a path is the sum of the node's values in the path.
Given the root of a binary tree, return the maximum path sum of any non-empty path.

Example 1:
Input: root = [1,2,3]
Output: 6
Explanation: The optimal path is 2 -> 1 -> 3 with a path sum of 2 + 1 + 3 = 6.

Example 2:
Input: root = [-10,9,20,null,null,15,7]
Output: 42
Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42.

Constraints:
The number of nodes in the tree is in the range [1, 3 * 104].
-1000 <= Node.val <= 1000
*/

/**
 * 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 {
public:
    int maxPathSum(TreeNode* root, int& maxSum){
        if (!root)
            return 0;
        int leftSum = max(maxPathSum(root -> left, maxSum), 0);
        int rightSum = max(maxPathSum(root -> right, maxSum), 0);
        maxSum = max(maxSum, leftSum + rightSum + root -> val);
        return max(leftSum, rightSum) + root -> val;
    }

    int maxPathSum(TreeNode* root) {
        if (!root)
            return 0;
        int maxSum = INT_MIN;
        maxPathSum(root, maxSum);
        return maxSum;
    }
};