←ENG-DSA-004CI/CD Pipeline Dependency Resolution (Graphs)
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CI/CD Pipeline Dependency Resolution (Graphs)

CompaniesGitLab, Vercel
Est. Time~40 min
LevelMid
GraphsTopological SortBFS
🚨 P0 Incident
GitLabVercel

GitLab's monorepo CI/CD system failed to build after a developer accidentally created a circular dependency between packages. The build runner hung indefinitely waiting for Package A (which waits for B, which waits for A). Before executing any build, the system must compute a valid topological order and fail fast if a cycle exists.

📥 Assigned to:You — Mid Engineer
Your Task

Our monorepo build system fails because packages depend on each other. Given packages and dependency pairs (A depends on B), return a valid build order. Raise an error if circular dependency exists.

⏱ Time: O(V + E)💾 Space: O(V + E)
Example 1
Input:  pkgs=['A','B','C'], deps=[('B','A'),('C','B')]
Output: ['A','B','C']
Example 2
Input:  pkgs=['X','Y','Z'], deps=[]
Output: Any order of X, Y, Z
🔒 +3 hidden test cases — revealed on Submit
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Test Output
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