Design a single-machine LRU cache

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Use PracHub's coding console to write, test, and debug your solutions in Python or JavaScript. View hints, test against sample inputs, and compare with official solutions.

Q: What difficulty level is this coding question?

This is a medium difficulty Coding & Algorithms question, commonly asked during Technical Screen rounds at DoorDash.

Q: What role is this question designed for?

This question is commonly asked for Software Engineer candidates at DoorDash during technical interviews.

Question

Design an in-memory LRU cache for a single machine using a hash map and a doubly linked list to support O(
1) get and put. Explain how you handle capacity, eviction, and key updates. Then make your design thread-safe: discuss lock granularity (global lock vs. per-bucket/segmented locks), readers–writer locks, lock-free alternatives, and how you would prevent race conditions and ensure memory safety. Analyze time and space complexity and outline major pitfalls.

PracHub · Accepted Answer

This question evaluates a candidate's ability to design an efficient in-memory LRU cache and apply concurrency control, covering eviction semantics, capacity management, key updates, and synchronization for thread safety.

Quick Overview

Design a single-machine LRU cache

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