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

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

Implement Cache and Key-Value Store

Quick Overview

This question evaluates the ability to design efficient in-memory data structures and caching mechanisms, focusing on core key-value operations, eviction behavior, and performance constraints.

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Part 2: Build an In-Memory Key-Value Store

Implement a simple in-memory key-value store for string keys and integer values. Process a sequence of operations and return the outputs of all get and delete operations. Supported operations are ('put', key, value), ('get', key), and ('delete', key). For the coding part, implement the store from scratch using a hash table with separate chaining and resizing; do not use Python's built-in dict as the main storage structure. Return None for a missing get, and return True or False for delete depending on whether the key existed. Follow-up discussion: compare this design with a second valid approach such as keeping entries in a sorted list and using binary search. A hash table gives average O(1) operations but needs collision handling and does not keep keys ordered; a sorted list gives O(log n) lookup and ordered traversal, but O(n) insertion and deletion.

Constraints

0 <= len(operations) <= 200000
Each key is a non-empty string with length <= 100
-10^9 <= value <= 10^9
Each operation is one of ('put', key, value), ('get', key), or ('delete', key)

Examples

Input: ([('put', 'a', 1), ('put', 'b', 2), ('get', 'a'), ('put', 'a', 3), ('get', 'a'), ('delete', 'b'), ('get', 'b'), ('delete', 'x')],)

Expected Output: [1, 3, True, None, False]

Explanation: Basic insert, update, lookup, successful delete, missing lookup, and failed delete.

Input: ([],)

Expected Output: []

Explanation: Edge case: no operations.

Input: ([('delete', 'ghost'), ('put', 'ghost', 7), ('get', 'ghost'), ('delete', 'ghost'), ('get', 'ghost'), ('delete', 'ghost')],)

Expected Output: [False, 7, True, None, False]

Explanation: Deleting a missing key returns False. After deletion, later get returns None.

Input: ([('put', 'k0', 0), ('put', 'k1', 1), ('put', 'k2', 2), ('put', 'k3', 3), ('put', 'k4', 4), ('put', 'k5', 5), ('put', 'k6', 6), ('get', 'k6'), ('get', 'k0'), ('delete', 'k3'), ('get', 'k3')],)

Expected Output: [6, 0, True, None]

Explanation: Several inserts force the table to handle more entries and still return correct values after updates and deletion.

Hints

Use an array of buckets, where each bucket stores a small list of (key, value) pairs.
If too many items are stored relative to the number of buckets, resize and rehash all existing entries to keep average operations fast.

Quick Overview