Optimize rotation for in-place
Last updated: March 13, 2026
Quick Overview
Given an array of integers, rotate the array in-place to the right by a specified number of steps. The function should modify the original array and return nothing, with the input being the array and the number of steps as parameters. Ensure the solution operates efficiently within O(n) time complexity and O(1) space complexity.
Doordash
March 13, 2026117
14
651 solved
Given an array of integers, rotate the array in-place to the right by a specified number of steps. The function should modify the original array and return nothing, with the input being the array and the number of steps as parameters. Ensure the solution operates efficiently within O(n) time complexity and O(1) space complexity.
This coding problem is frequently asked during Technical Screen at Doordash. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Doordash 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 in a single pass?
- How would you test this solution thoroughly?
- How would you parallelize this solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
To solve the problem of rotating an array in-place, we can recognize that this is a variation of a cyclic rotation problem. The primary pattern that applies here is the use of the 'reverse' approach, ...
Approach
- Normalize the Rotation Steps: First, since rotating an array by its length results in the same array, we can reduce the number of rotation steps by taking
k % n, wherenis the length of th...
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