Two Pointers on matrix
Last updated: December 20, 2025
Quick Overview
Given a 2D matrix of integers, implement the two pointers technique to find the maximum sum of a subarray of size k within the matrix. Your function should return the maximum sum and the starting coordinates of the subarray. The input will be a matrix of size m x n and an integer k, where 1 ≤ k ≤ min(m, n).
CrowdStrike
December 20, 202510
15
1,157 solved
Given a 2D matrix of integers, implement the two pointers technique to find the maximum sum of a subarray of size k within the matrix. Your function should return the maximum sum and the starting coordinates of the subarray. The input will be a matrix of size m x n and an integer k, where 1 ≤ k ≤ min(m, n).
CrowdStrike uses this problem in the Technical 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
- How would you test this solution thoroughly?
- What is the worst-case input for your solution?
- How would you modify your solution to handle streaming input?
- Can you solve this iteratively instead of recursively (or vice versa)?
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Practice DSA ProblemsSample Answer
Problem Analysis
In this problem, we need to find the maximum sum of a subarray of size k within a 2D matrix. The two pointers technique is applicable here because we can maintain a sliding window of size k to efficie...
Approach
- Initialize variables to store the maximum sum found (
max_sum), the starting coordinates of the subarray (start_row,start_col), and a variable to keep track of the current sum. - Iterate thr...
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