Two Pointers on matrix
Last updated: February 8, 2026
Quick Overview
Given a 2D matrix of integers, implement the Two Pointers technique to find the maximum sum of a rectangle formed by any two rows and two columns. Your function should take the matrix as input and return the maximum sum as output. The solution should efficiently handle matrices of varying dimensions and values, ensuring optimal performance.
Apple
February 8, 2026173
7
1,478 solved
Given a 2D matrix of integers, implement the Two Pointers technique to find the maximum sum of a rectangle formed by any two rows and two columns. Your function should take the matrix as input and return the maximum sum as output. The solution should efficiently handle matrices of varying dimensions and values, ensuring optimal performance.
Coding interviews at Apple focus on problem-solving approach as much as the final solution. The interviewer wants to see you break down the problem, consider edge cases, and optimize iteratively. Communication throughout the process is key.
What the Interviewer Expects
- Quickly identify the optimal approach and its theoretical basis
- Handle complex algorithm design with multiple interacting components
- Write concise, elegant code under time pressure
- Prove correctness of your approach and discuss alternative solutions
- Optimize beyond the obvious: discuss constant factor improvements
- Address follow-up variations and explain how the solution generalizes
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
- Can you optimize the space complexity of your solution?
- What is the worst-case input for your solution?
- How would you parallelize this solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem requires us to find the maximum sum of a rectangle defined by any two rows and two columns in a 2D matrix. The Two Pointers technique is suitable here because it allows us to efficiently e...
Approach
- Initialize Variables: Create a variable
max_sumto track the maximum rectangle sum found. - Iterate Over Row Pairs: Use two nested loops to select two rows
r1andr2. For each pair...
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