Optimize inversion for in-place
Last updated: February 12, 2026
Quick Overview
Given an array of integers, write a function to invert the elements of the array in-place, such that the first element becomes the last, the second element becomes the second to last, and so on. Your solution should operate within O(1) space complexity and should modify the original array directly. The function should return the modified array after inversion.
Compass
February 12, 202635
12
961 solved
Given an array of integers, write a function to invert the elements of the array in-place, such that the first element becomes the last, the second element becomes the second to last, and so on. Your solution should operate within O(1) space complexity and should modify the original array directly. The function should return the modified array after inversion.
This coding problem is frequently asked during Take-home Project at Compass. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Compass 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
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 in a single pass?
- What is the worst-case input for your solution?
- How would you modify your solution to handle streaming input?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem requires us to invert an array of integers in-place, meaning we need to reverse the order of the elements without using any additional storage that grows with the input size. The optimal a...
Approach
- Initialize two pointers: one at the start of the array (
left) and one at the end (right). - While
leftis less thanright, perform the following steps:- Swap the elements at the
left...
- Swap the elements at the
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