Time-Based Key-Value Store with Production Testing

Problem Overview

Design and implement a time-based key-value data structure that stores multiple values for the same key at different timestamps and retrieves values based on temporal queries. Unlike the LeetCode version, this interview uses real timestamps (Unix epoch seconds as floats or datetime objects) rather than monotonically increasing integers. The main challenge extends beyond basic implementation to production-grade concerns: writing comprehensive tests, mocking time, ensuring timestamp ordering guarantees, and handling concurrent access with appropriate locking strategies.

Part 1: Basic Implementation with Real Timestamps

Implement a TimeMap class that stores key-value pairs with real timestamp values and supports temporal queries.

Requirements

• Constructor: TimeMap() - Initializes the data structure
• Set Operation: set(key: str, value: str, timestamp: float) - Stores the key with the given value at the specified timestamp
• timestamp is a real Unix timestamp (seconds since epoch) as a float
• Multiple values can be stored for the same key at different timestamps
• Timestamps for the same key may not arrive in order
• Get Operation: get(key: str, timestamp: float) -> str - Returns the value where set was called previously with timestamp_prev <= timestamp
• If multiple values exist, return the one with the largest timestamp_prev
• Return empty string "" if no such value exists
• Must be efficient for frequent queries

Example Usage

`from datetime import datetime import time timemap = TimeMap()

Store values with real timestamps

t1 = time.time() # e.g., 1678901234.567 timemap.set("user:1:status", "online", t1) time.sleep(0.1) t2 = time.time() $L41 $L43 timemap.get($L44, t2) == $L45 t3 = time.time() timemap.$L47($L48, $L49, t3) $L4b timemap.get($L4c, t2 + $L4d) == $L4e $L50 timemap.get($L51, t3) == $L52 $L54 timemap.get($L55, t1 - $L56) == $L57 $L59 timemap.get($L5a, t3) == $L5b