Find cycle in graph
Last updated: September 29, 2025
Quick Overview
Given a directed or undirected graph, determine if there is a cycle present in the graph. You should implement a function that takes the graph as input in the form of an adjacency list and returns a boolean value indicating whether a cycle exists.
Discord
September 29, 202548
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Given a directed or undirected graph, determine if there is a cycle present in the graph. You should implement a function that takes the graph as input in the form of an adjacency list and returns a boolean value indicating whether a cycle exists.
Coding interviews at Discord 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 test this solution thoroughly?
- What happens if the input contains duplicates?
- How would you parallelize this solution?
- What if the input doesn't fit in memory?
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Practice DSA ProblemsSample Answer
Problem Analysis
To determine if there is a cycle in a directed or undirected graph, we can utilize Depth-First Search (DFS) with a technique to track visited nodes. The key pattern here is to maintain a record of nod...
Approach
- Create a function
has_cycle(graph)that initializes a visited set and a recursion stack. - Iterate through each node in the graph:
- If the node has not been visited, call the helper function...
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