LeetCode 124. Binary Tree Maximum Path Sum

Tree

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 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

Solution

class Solution {
    
    int dfs(TreeNode *root, int& result) {
        if (root == nullptr) {
            return 0;
        }

        int l = max(0, dfs(root->left, result));
        int r = max(0, dfs(root->right, result));
        result = max(result, l + r + root->val);

        return root->val + max(l, r);
    }
    
public:
    int maxPathSum(TreeNode *root) {
        int result = INT_MIN;
        dfs(root, result);
        return result;
    }
};