Software Engineer · Full Journey · Multiple Types

Citadel — Software Engineer ✅ Passed

Level: Intern

Round: Full Journey · Type: Multiple Types · Difficulty: 7/10 · Duration: 240 min · Interviewer: Unfriendly

Topics: Data Structures, Algorithms, System Design, Object-Oriented Design, Priority Queue, Binary Indexed Tree

Location: Miami, FL

Interview date: 2026-01-20

Summary

Round 1: Coding

Question: Implement a 2048 simulation and encode/decode compression into a long long.

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Round 2: Coding

Question: Implement insert and delete operations on a weighted data structure, supporting random sampling by weight. I implemented a doubling binary indexed tree with dynamic expansion.

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Round 3: System Design & OOD

Question: Design a system that supports inserting a relation where each application can correspond to multiple exchanges, and there's an alert if an exchange corresponds to too many applications. I implemented a sliding window. Follow-up questions covered parallel distributed systems with various control conditions.

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Round 4: Coding

Question: Implement insert, delete, and execute task operations. I used a priority queue with lazy deletion.

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Details

Preparation Tips & Key Takeaways

What I Learned

• I learned to solidify my understanding of data structures like binary indexed trees and priority queues.
• I need to be prepared to discuss the design and scaling of systems in a distributed environment.

Recommended Preparation

Coding Practice

• Practice implementing variations of binary indexed trees.
• Strengthen understanding of priority queue implementations and lazy deletion strategies.

System Design

• Review common patterns like sliding windows.
• Study distributed systems concepts, including different control conditions and parallel processing.

Behavioral Questions

• Prepare examples related to problem-solving and system design decisions.

Resources I Recommend

• LeetCode for coding practice.
• System design interview prep resources.

LeetCode similar: LeetCode 2048