Topological Sort of Cloud Resource Dependencies
Last updated: December 9, 2025
Quick Overview
Given cloud resources with dependencies (VPCs contain subnets, subnets contain instances, instances use security groups), produce a valid deletion order that respects dependencies. Handle circular dependencies gracefully.
Wiz
December 9, 20259
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Given cloud resources with dependencies (VPCs contain subnets, subnets contain instances, instances use security groups), produce a valid deletion order that respects dependencies. Handle circular dependencies gracefully.
Cloud resource cleanup and decommissioning requires deleting resources in the right order. You cannot delete a VPC before deleting the subnets inside it, and you cannot delete a subnet before deleting the instances in it. This is a classic topological sort problem with the real-world twist of handling circular dependencies that sometimes exist in cloud environments.
What the Interviewer Expects
- Implement topological sort using Kahn's algorithm (BFS) or DFS
- Detect and handle circular dependencies instead of crashing
- Return a valid deletion order (reverse topological order)
- Handle multiple valid orderings correctly
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 if some resources can be deleted in parallel? How would you maximize parallelism?
- How would you handle a circular dependency between a security group and an instance?
- Can you modify your solution to handle weighted dependencies (some deletions take longer)?
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Problem Analysis
This problem involves creating a valid deletion order for cloud resources that have dependencies, which is a classic topological sorting problem. We will use Kahn's algorithm, which is based on BFS, b...
Approach
- Graph Representation: Model the resources as a directed graph where nodes represent resources and edges represent dependencies. For instance, if a subnet (S2) depends on a VPC (V1), there will ...
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