LeetCode 124: Binary Tree Maximum Path Sum

Question

I'm posting my code for a LeetCode problem. If you'd like to review, please do so. Thank you for your time!

Problem

Given a non-empty binary tree, find the maximum path sum.

For this problem, a path is defined as any sequence of nodes from some starting node to any node in the tree along the parent-child connections. The path must contain at least one node and does not need to go through the root.

Example 1:

Input: [1,2,3] 1 / \ 2 3 Output: 6 

Example 2:

Input: [-10,9,20,null,null,15,7] -10 / \ 9 20 / \ 15 7 Output: 42 

Inputs

[1,2,3] [-10,9,20,null,null,15,7] [-10,9,20,null,null,15,7,9,20,null,null,15,7] [-10,9,20,null,null,15,7,9,20,null,null,15,720,null,null,15,7,9,20,null,null,15,7] [-10,9,20,null,null,15,7,9,20,null,null,15,720,null,null,15,7,9,20,null,null,15,7999999,20,null,null,15,7,9,20,null,null,15,720,null,null,15,7,9,20,null,null,15,7] 

Outputs

6 42 66 791 8001552 

Code

#include <cstdint> #include <algorithm> struct Solution { int maxPathSum(TreeNode* root) { std::int_fast64_t sum = INT_FAST64_MIN; depthFirstSearch(root, sum); return sum; } private: static std::int_fast64_t depthFirstSearch( const TreeNode* node, std::int_fast64_t& sum ) { if (!node) { return 0; } const std::int_fast64_t left = std::max( (std::int_fast64_t) 0, depthFirstSearch(node->left, sum) ); const std::int_fast64_t right = std::max( (std::int_fast64_t) 0, depthFirstSearch(node->right, sum) ); sum = std::max(sum, left + right + node->val); return std::max(left, right) + node->val; } }; 

References

• Problem

• Discuss

• Solution

Answer 1

There's not much to say about your answer, it looks fine! One could quibble over the names of variables, maybe left and right could be named left_sum and right_sum for example, and you could've used auto for the type of those two variables. But other than that I think there is nothing that can be improved.

Answer 2

Not sure why you decided to use std::int_fast64_t over the common int that is used as the type of the tree nodes values.

But since you did, it would be more idiomatic to do at least:

static_cast<std::int_fast64_t>(0); 

instead of

(std::int_fast64_t) 0;