Optimize flattening for with follow-up

Last updated: March 12, 2026

Quick Overview

Find an efficient solution for compression given the with follow-up constraint.

Apple
Coding & Algorithms
Machine Learning Engineer
Apple
March 12, 2026
Machine Learning Engineer
Take-home Project
Coding & Algorithms
Hard

49

3

1,869 solved


Find an efficient solution for compression given the with follow-up constraint.

This coding problem is frequently asked during Take-home Project 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
Hash maps and frequency counting
Common algorithm patterns (sliding window, two pointers, BFS/DFS)
Graph algorithms and traversal
Tree structures and recursion
Time and space complexity analysis
Dynamic programming and memoization
How to Approach This
  1. Clarify input constraints and edge cases before writing code.
  2. Walk through your approach verbally and confirm with the interviewer before coding.
  3. Start with a brute force solution, then optimize. Mention time and space complexity.
  4. Test your solution with examples, including edge cases like empty input or duplicates.
  5. Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
Possible Follow-up Questions
  • How would you test this solution thoroughly?
  • How would you modify your solution to handle streaming input?
  • How would your solution change if the input was sorted?
  • How would you parallelize this solution?
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