Optimize partitioning for O(n) time
Last updated: July 24, 2025
Quick Overview
Given an array of integers, partition the array in such a way that all elements less than a specified pivot are on the left, and all elements greater than the pivot are on the right, achieving this in O(n) time complexity. The partitioning should be done in-place, and the relative order of the elements does not need to be maintained. Return the indices of the pivot after partitioning.
Lyft
July 24, 20256
9
2,794 solved
Given an array of integers, partition the array in such a way that all elements less than a specified pivot are on the left, and all elements greater than the pivot are on the right, achieving this in O(n) time complexity. The partitioning should be done in-place, and the relative order of the elements does not need to be maintained. Return the indices of the pivot after partitioning.
This coding problem is frequently asked during Technical Screen at Lyft. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Lyft expects candidates to write production-quality code, not just solve the puzzle.
What the Interviewer Expects
- Recognize the underlying problem pattern (sliding window, two pointers, BFS/DFS, etc.)
- Discuss multiple approaches and trade-offs before coding
- Implement an optimal solution with clean, production-quality code
- Handle all edge cases including boundary conditions and invalid input
- Optimize both time and space complexity with clear justification
- Test your solution systematically with well-chosen examples
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 iteratively instead of recursively (or vice versa)?
- Can you solve this in a single pass?
- How would you parallelize this solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem requires us to partition an array around a specified pivot such that elements less than the pivot are to its left, and those greater than the pivot are to its right. This can be efficientl...
Approach
- Initialize two pointers: one (
left) at the start of the array and the other (right) at the end. - While the
leftpointer is less than or equal to therightpointer:- If the element at ...
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