Optimize partitioning for in-place
Last updated: December 19, 2025
Quick Overview
Given an array of integers, implement an in-place algorithm to optimize the partitioning of the array around a pivot element. The algorithm should rearrange the elements so that all elements less than the pivot come before it, and all elements greater than the pivot come after it, while maintaining the original order of equal elements. The function should return the modified array.
HRT
December 19, 2025113
10
160 solved
Given an array of integers, implement an in-place algorithm to optimize the partitioning of the array around a pivot element. The algorithm should rearrange the elements so that all elements less than the pivot come before it, and all elements greater than the pivot come after it, while maintaining the original order of equal elements. The function should return the modified array.
HRT uses this problem in the Take-home Project 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
- 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
- How would your solution change if the input was sorted?
- How would you test this solution thoroughly?
- Can you solve this in a single pass?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem is a variant of the classic partitioning problem, where we need to rearrange elements around a pivot while maintaining the relative order of equal elements. A suitable pattern for this pro...
Approach
- Initialization: Start with two pointers:
lessinitialized to the beginning of the array andgreaterinitialized to the end of the array. - Traversal: Iterate through the array with a ...
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