124. Binary Tree Maximum Path Sum

[jason89521]

Practice Dates

• 2024/05/16

Description

Link: https://leetcode.com/problems/binary-tree-maximum-path-sum/description/

Solution

Use post-order traversal to calculate the maximum path sum.

/**
 * 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 maxVal = 0;
        bool hasInit = false;
        traversal(root, maxVal, hasInit);

        return maxVal;
    }

    int traversal(TreeNode* root, int& maxVal, bool& hasInit) {
        if (root == nullptr) {
            return 0;
        }

        auto left = traversal(root->left, maxVal, hasInit);
        if (left < 0) {
            left = 0;
        }
        auto right = traversal(root->right, maxVal, hasInit);
        if (right < 0) {
            right = 0;
        }
        auto maxPath = (std::max(left, right) + root->val);
        if (!hasInit) {
            hasInit = true;
            maxVal = maxPath;
        } else {
            maxVal = std::max(maxVal, left + right + root->val);
        }

        return maxPath;
    }
};

Performance

Time complexity: