Rate Limiter Implementation

Difficulty: Medium
Estimated Time: 30-45 minutes
Tags: System Design, TypeScript, Sliding Window, Data Structures
Source: Real Interview Question

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Problem Statement

Implement a rate limiter class in TypeScript (or your chosen language) that restricts a given user to a maximum number of requests in a given time window (e.g., 100 requests per minute).

For now, assume this code runs on a single server.

Write a test function to show that your logic works.

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Requirements

• Create a RateLimiter class
• Support configurable max requests and time window
• Track requests per user (by user ID)
• Return true if request is allowed, false if rate limited
• Include a test function demonstrating the functionality

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Example Usage

const limiter = new RateLimiter(100, 60000); // 100 requests per minute

limiter.allowRequest('user123'); // true
limiter.allowRequest('user123'); // true
// ... after 100 requests
limiter.allowRequest('user123'); // false (rate limited)

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Constraints

• Single server (no distributed considerations)
• Time window is sliding (not fixed buckets)
• Memory efficient for many users
• O(1) or O(log n) time complexity for allowRequest