Transform matrix to hash map
Last updated: May 3, 2026
Quick Overview
Given a matrix of integers, transform it into a hash map where the keys are the unique integers from the matrix and the values are the counts of their occurrences. The output should be a hash map that accurately reflects the frequency of each integer in the input matrix.
Airbnb
May 3, 202629
8
1,340 solved
Given a matrix of integers, transform it into a hash map where the keys are the unique integers from the matrix and the values are the counts of their occurrences. The output should be a hash map that accurately reflects the frequency of each integer in the input matrix.
This coding problem is frequently asked during Phone Screen at Airbnb. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Airbnb 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
- How would your solution change if the input was sorted?
- What happens if the input contains duplicates?
- How would you parallelize this solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
To transform a matrix of integers into a hash map (or dictionary in Python), we will apply a counting approach using a hash map to track occurrences of unique integers. The problem can be efficiently ...
Approach
- Initialize an empty hash map (dictionary) to store integer counts.
- Iterate through each row of the matrix.
- For each integer in the row, check if it exists in the hash map:
- If it exists, ...
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