Optimize inversion for without recursion

Last updated: January 22, 2026

Quick Overview

Find an efficient solution for flattening given the without recursion constraint.

Waymo
Coding & Algorithms
Software Engineer
Waymo
January 22, 2026
Software Engineer
Onsite
Coding & Algorithms
Easy

43

14

1,398 solved


Find an efficient solution for flattening given the without recursion constraint.

This coding problem is frequently asked during Onsite at Waymo. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Waymo expects candidates to write production-quality code, not just solve the puzzle.

What the Interviewer Expects
  • Identify the correct data structure and algorithm for the problem
  • Write clean, bug-free code with proper variable naming
  • Analyze time and space complexity correctly
  • Handle basic edge cases (empty input, single element)
  • Communicate your thought process while coding
Key Topics to Cover
Data structure selection and trade-offs
Dynamic programming and memoization
Hash maps and frequency counting
Time and space complexity analysis
Binary search and divide and conquer
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
  • Can you solve this iteratively instead of recursively (or vice versa)?
  • What if the input doesn't fit in memory?
  • Can you optimize the space complexity of your solution?
  • How would your solution change if the input was sorted?
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