Count minimum cost in binary tree
Last updated: August 13, 2025
Quick Overview
Given a binary tree, calculate the minimum cost to reach from the root to any leaf node, where the cost is defined as the sum of the values of the nodes along the path. You need to implement a function that takes the root of the binary tree as input and returns the minimum cost as an integer.
Brex
August 13, 2025141
15
1,669 solved
Given a binary tree, calculate the minimum cost to reach from the root to any leaf node, where the cost is defined as the sum of the values of the nodes along the path. You need to implement a function that takes the root of the binary tree as input and returns the minimum cost as an integer.
Brex uses this problem in the Phone Screen to evaluate your algorithmic thinking. They expect you to discuss multiple approaches, analyze trade-offs between them, and implement the optimal solution with clean, readable code.
What the Interviewer Expects
- Recognize the underlying problem pattern (sliding window, two pointers, BFS/DFS, etc.)
- Discuss multiple approaches and trade-offs before coding
- Implement an optimal solution with clean, production-quality code
- Handle all edge cases including boundary conditions and invalid input
- Optimize both time and space complexity with clear justification
- Test your solution systematically with well-chosen examples
Key Topics to Cover
How to Approach This
- Clarify input constraints and edge cases before writing code.
- Walk through your approach verbally and confirm with the interviewer before coding.
- Start with a brute force solution, then optimize. Mention time and space complexity.
- Test your solution with examples, including edge cases like empty input or duplicates.
- Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
Possible Follow-up Questions
- What if the input doesn't fit in memory?
- Can you optimize the space complexity of your solution?
- How would you parallelize this solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
This problem is best approached using Depth-First Search (DFS) since we need to explore all paths from the root to each leaf node in the binary tree. The goal is to compute the minimum cost, defined a...
Approach
- Initialize a variable to store the minimum cost (set initially to infinity).
- Define a recursive DFS function that takes the current node and the cumulative cost as parameters.
- **B...
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