Implement LRU Cache with streaming input
Last updated: February 4, 2026
Quick Overview
Implement a Stack data structure that supports insert, delete, and lookup operations in O(n) time.
Twitter/X
February 4, 20265
4
181 solved
Implement a Stack data structure that supports insert, delete, and lookup operations in O(n) time.
Twitter/X uses this problem in the Take-home Project to evaluate your algorithmic thinking. They expect you to discuss multiple approaches, analyze trade-offs between them, and implement the optimal solution with clean, readable code.
What the Interviewer Expects
- Recognize the underlying problem pattern (sliding window, two pointers, BFS/DFS, etc.)
- Discuss multiple approaches and trade-offs before coding
- Implement an optimal solution with clean, production-quality code
- Handle all edge cases including boundary conditions and invalid input
- Optimize both time and space complexity with clear justification
- Test your solution systematically with well-chosen examples
Key Topics to Cover
How to Approach This
- Clarify input constraints and edge cases before writing code.
- Walk through your approach verbally and confirm with the interviewer before coding.
- Start with a brute force solution, then optimize. Mention time and space complexity.
- Test your solution with examples, including edge cases like empty input or duplicates.
- Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
Possible Follow-up Questions
- Can you optimize the space complexity of your solution?
- Can you solve this iteratively instead of recursively (or vice versa)?
- What if the input doesn't fit in memory?
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Practice DSA ProblemsSample Answer
Problem Analysis
The task requires implementing a Least Recently Used (LRU) Cache, which is a common design problem for optimizing memory usage. The underlying pattern for this problem is a combination of a hash map (...
Approach
- Data Structures: Use a hash map (
cache) to store key-value pairs, where the key is the identifier and the value is a reference to the node in the doubly linked list. Use a doubly linked list ...
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