Find cycle in array
Last updated: December 18, 2025
Quick Overview
Given an array of integers where each element represents the number of steps to jump forward in the array, determine if there is a cycle in the array. A cycle occurs if you can start from any index and eventually return to that index by following the jumps. The function should return true if a cycle exists and false otherwise.
Shopify
December 18, 202511
6
2,078 solved
Given an array of integers where each element represents the number of steps to jump forward in the array, determine if there is a cycle in the array. A cycle occurs if you can start from any index and eventually return to that index by following the jumps. The function should return true if a cycle exists and false otherwise.
Coding interviews at Shopify focus on problem-solving approach as much as the final solution. The interviewer wants to see you break down the problem, consider edge cases, and optimize iteratively. Communication throughout the process is key.
What the Interviewer Expects
- Identify the correct data structure and algorithm for the problem
- Write clean, bug-free code with proper variable naming
- Analyze time and space complexity correctly
- Handle basic edge cases (empty input, single element)
- Communicate your thought process while coding
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 you modify your solution to handle streaming input?
- Can you solve this iteratively instead of recursively (or vice versa)?
- What is the worst-case input for your solution?
- How would you parallelize this solution?
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Problem Analysis
To solve the problem of detecting a cycle in an array where each element represents the number of steps to jump forward, we can use the Floyd's Tortoise and Hare algorithm (also known as the cycle...
Approach
- Initialize two pointers: Start with two pointers,
slowandfast, both set to the first index of the array (index 0). - Move the pointers: In a loop, advance
slowby one step and `fas...
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