Optimize compression for without recursion
Last updated: November 19, 2025
Quick Overview
Given a string, implement a function to optimize its compression by replacing consecutive repeated characters with a single character followed by the count of repetitions, without using recursion. The function should take a string as input and return the compressed string as output, ensuring that the output is shorter than the original string when possible.
Elastic
November 19, 20254
7
4,666 solved
Given a string, implement a function to optimize its compression by replacing consecutive repeated characters with a single character followed by the count of repetitions, without using recursion. The function should take a string as input and return the compressed string as output, ensuring that the output is shorter than the original string when possible.
This coding problem is frequently asked during Phone Screen at Elastic. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Elastic expects candidates to write production-quality code, not just solve the puzzle.
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 is the worst-case input for your solution?
- Can you solve this in a single pass?
- How would you parallelize this solution?
- Can you solve this iteratively instead of recursively (or vice versa)?
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Problem Analysis
The problem requires compressing a string by replacing consecutive repeated characters with a single character followed by the count of repetitions. The pattern that applies here is the **two pointers...
Approach
- Initialize two pointers:
ifor iterating through the string andjfor tracking the start of a sequence of repeated characters. - Create a list
compressedto build the output string. - Loop ...
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