Optimize compression for with follow-up
Last updated: July 11, 2025
Quick Overview
Given a string of characters, implement an algorithm to optimize the compression of the string such that consecutive repeating characters are represented by a single character followed by the count of repetitions. For example, the input "aabbcc" should be compressed to "a2b2c2". Additionally, provide a follow-up solution that handles edge cases, such as strings that are already compressed or contain non-alphabetic characters. The output should be the compressed string.
Doordash
July 11, 202542
5
1,756 solved
Given a string of characters, implement an algorithm to optimize the compression of the string such that consecutive repeating characters are represented by a single character followed by the count of repetitions. For example, the input "aabbcc" should be compressed to "a2b2c2". Additionally, provide a follow-up solution that handles edge cases, such as strings that are already compressed or contain non-alphabetic characters. The output should be the compressed string.
Doordash uses this problem in the Take-home Project 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
- What happens if the input contains duplicates?
- How would you parallelize this solution?
- How would you test this solution thoroughly?
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Practice DSA ProblemsSample Answer
Problem Analysis
This problem can be approached using a two pointers technique or a simple iterative approach. The primary task is to traverse the string while counting consecutive repeating characters. The tw...
Approach
- Initialize an empty result string and a count variable.
- Iterate through the string using a loop.
- For each character, compare it with the next character:
- If they are the same, incremen...
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