← Citadel Interview Insights

Citadel·Software Engineer·Technical Phone Screen·Junior

JuniorRejected
Sep 2026

Summary

Went into a Citadel SWE intern round completely cold, no leetcode prep, and got hit with a stateful data structure plus object-oriented design problem that had an optimization component baked in. Got maybe halfway through before time ran out and the interviewer was visibly checked out, phone in hand, mic picking up background noise the whole time. Not great.

Questions Asked (1)

Q1

Design and implement a custom stateful data structure with object-oriented principles and a greedy optimization component, adjusting your approach as new constraints are introduced mid-problem.

Algorithms & Data StructuresSystem DesignTechnical Trade-offs
Author's notes

I went in expecting a standard algorithm question and got something completely different.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, then design a class hierarchy that encapsulates state and operations. Implement the greedy component with a clear invariant, and be prepared to refactor as new constraints are introduced, explaining trade-offs at each step.

Pro tip: Verbalize your thought process and explicitly state assumptions; interviewers at Citadel value structured reasoning and adaptability over perfect code. When constraints change, pause to reassess the design before coding, showing you can pivot without panic.

1. Clarify Requirements and Constraints

Ask questions to understand the data structure's expected operations, performance requirements, and any initial constraints. Confirm the greedy optimization goal and how new constraints might be introduced.

2. Design Object-Oriented Skeleton

Outline classes, interfaces, and key methods, focusing on encapsulation and separation of concerns. Explain how state will be maintained and updated.

3. Implement Greedy Component

Describe the greedy algorithm, including the selection criterion and proof of correctness or invariant. Discuss how it integrates with the data structure.

4. Adapt to New Constraints

When new constraints are introduced, analyze their impact on the current design. Propose modifications, such as changing data structures or algorithm, and explain trade-offs.

5. Test and Validate

Walk through test cases, including edge cases and performance under new constraints. Verify correctness and efficiency, and suggest potential improvements.

Key Points to Mention

  • Encapsulation and abstraction in class design
  • Greedy algorithm correctness and invariant maintenance
  • Time and space complexity analysis
  • Trade-offs between different data structures (e.g., arrays vs. trees vs. heaps)
  • Handling dynamic constraints and refactoring
  • Testing strategies for stateful structures

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.