Detect permutation in matrix
Last updated: November 8, 2025
Quick Overview
Given a matrix of integers, determine if any row or column contains a permutation of a given target array. The input consists of the matrix and the target array, and the output should be a boolean indicating whether such a permutation exists in the matrix.
Shopify
November 8, 20252
12
1,679 solved
Given a matrix of integers, determine if any row or column contains a permutation of a given target array. The input consists of the matrix and the target array, and the output should be a boolean indicating whether such a permutation exists in the matrix.
This coding problem is frequently asked during Onsite at Shopify. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Shopify 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
- Can you solve this in a single pass?
- Can you optimize the space complexity of your solution?
- What if the input doesn't fit in memory?
- How would you test this solution thoroughly?
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Problem Analysis
To determine if any row or column in the matrix contains a permutation of the target array, we can leverage a hashmap (or dictionary in Python) to count the occurrences of each integer in the targ...
Approach
- Count Frequencies of Target Array: Create a frequency dictionary for the integers in the target array.
- Example: for target = [1, 2, 2], freq = {1: 1, 2: 2}.
- Check Rows: For each row...
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