Find longest subsequence in grid
Last updated: September 14, 2025
Quick Overview
Given a matrix, find the minimum cost efficiently using Sliding Window.
Apple
September 14, 202541
3
170 solved
Given a matrix, find the minimum cost efficiently using Sliding Window.
This coding problem is frequently asked during Phone Screen at Apple. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Apple expects candidates to write production-quality code, not just solve the puzzle.
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
- What is the worst-case input for your solution?
- How would your solution change if the input was sorted?
- How would you modify your solution to handle streaming input?
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Practice DSA ProblemsSample Answer
Problem Analysis
This prompt is slightly under-specified, so in an interview I would first restate the concrete version I am solving: > Given an `m x n` matrix of non...
Approach
Flattening the matrix conceptually gives us a one-dimensional stream, but we do **not** need to physically create a flattened list. That would add unn...
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