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Determine a Valid Course Completion Order

Given a number of courses and a list of prerequisite pairs, determine a valid order to complete all courses, or report that no valid order exists.

Practice in Interview Dashboard

1. Problem Statement

You are given a number of courses labeled 0 to n-1 and a list of prerequisite pairs [course, prereq] meaning prereq must be completed before course. Return a valid order to complete all courses, or an empty list if it is impossible.

2. Live Coding Format

Work in the provided coding workspace while explaining your decisions to the live interviewer. Validation may use inline tests, examples, comments, or a verbal walkthrough.

3. Key Focus Areas

  • 1
    Problem clarification and contract
  • 2
    Approach exploration and optimality
  • 3
    Think-aloud communication and pacing
  • 4
    Implementation correctness
  • 5
    Code quality and language fluency
  • 6
    Tests and dry run
  • 7
    Debugging and self-correction
  • 8
    Complexity analysis
  • 9
    Follow-up performance

4. What Strong Candidates Should Demonstrate

  • Clarify prerequisite direction, duplicate pairs, and impossible-order behavior before coding.
  • Explain a naive baseline and improve it to a linear-time approach that also detects when no order exists.
  • Think aloud while implementing readable, correct ordering logic.
  • Validate with explicit expected outputs and a top-to-bottom dry run.
  • Analyze time and space complexity and handle a bounded follow-up modification.

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Practice this problem in the live coding workspace while the interviewer probes your clarification, implementation, trade-offs, and validation.

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Core Concepts

Hidden because they name the technique, which a real interviewer would not tell you.

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GraphsTopological SortCycle DetectionComplexity Analysis

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