Optimize rotation for in-place
Last updated: June 7, 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 array directly and return nothing, ensuring that the rotation is done efficiently without using extra space. For example, given the input array [1, 2, 3, 4, 5] and steps = 2, the output should be [4, 5, 1, 2, 3].
MongoDB
June 7, 202681
4
3,276 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 array directly and return nothing, ensuring that the rotation is done efficiently without using extra space. For example, given the input array [1, 2, 3, 4, 5] and steps = 2, the output should be [4, 5, 1, 2, 3].
This coding problem is frequently asked during Phone Screen at MongoDB. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. MongoDB 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
- What happens if the input contains duplicates?
- How would you test this solution thoroughly?
- How would you modify your solution to handle streaming input?
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Practice DSA ProblemsSample Answer
Problem Analysis
This problem can be analyzed using the Reverse Method for array rotation, which efficiently rotates an array in-place without requiring extra space. The key insight is that rotating an array to th...
Approach
The steps to rotate the array in-place by k positions are as follows:
- Normalize Steps: If
kis greater than the length of the array, reducekusingk = k % len(array). This handles case...
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