Optimize flattening for in-place
Last updated: September 23, 2025
Quick Overview
Find an efficient solution for flattening given the in-place constraint.
Optiver
Coding & Algorithms
Software Engineer
Optiver
September 23, 2025Software Engineer
Onsite
Coding & Algorithms
Easy
46
5
2,879 solved
Find an efficient solution for flattening given the in-place constraint.
Optiver uses this problem in the Onsite 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
- 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
Hash maps and frequency counting
Sorting and searching
Binary search and divide and conquer
Graph algorithms and traversal
Common algorithm patterns (sliding window, two pointers, BFS/DFS)
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
- Can you solve this iteratively instead of recursively (or vice versa)?
- What is the worst-case input for your solution?
- Can you optimize the space complexity of your solution?
- How would your solution change if the input was sorted?
Sharpen Your Skills on Codemia
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Practice DSA ProblemsSample Answer
Problem Analysis
In this problem, we need to flatten a nested structure in-place, meaning we cannot use additional data structures that grow with input size. The most applicable pattern here is the Two Pointers te...
Approach
- Initialization: Start with two pointers:
i, which iterates through the list, andj, which marks the position for the next write. - Iterate through the structure: For each element poin...
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