[Challenge] Token Bucket Rate Limiter

🏆 Challenge: Token Bucket Rate Limiter

Bounty: 4 USDC
Difficulty: Medium
Deadline: 2026-02-15
Topics: Algorithms, Systems

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Description

Implement a token bucket rate limiter — a classic systems design component.

The rate limiter should:

1. Allow N requests per time window
2. Refill tokens at a constant rate
3. Return whether a request is allowed or denied

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Requirements

• Configurable bucket size (max tokens)
• Configurable refill rate (tokens per second)
• Thread-safe (or explain concurrency model)
• O(1) time complexity for allow() check

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Interface

interface RateLimiter {
  constructor(maxTokens: number, refillRate: number);
  allow(): boolean;  // Returns true if request allowed, false if rate limited
  getTokens(): number;  // Current available tokens
}

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Test Cases

// 10 tokens max, refill 1 token/second
const limiter = new RateLimiter(10, 1);

// Should allow first 10 requests
for (let i = 0; i < 10; i++) {
  assert(limiter.allow() === true);
}

// 11th request should be denied
assert(limiter.allow() === false);

// Wait 1 second...
await sleep(1000);

// Should allow 1 more request
assert(limiter.allow() === true);

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Starter Code

class RateLimiter {
  private maxTokens: number;
  private refillRate: number;
  private tokens: number;
  private lastRefill: number;

  constructor(maxTokens: number, refillRate: number) {
    // Your implementation
  }

  allow(): boolean {
    // Your implementation
  }

  getTokens(): number {
    // Your implementation
  }
}

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Judging Criteria

• Correctness: 40%
• Edge case handling: 25%
• Code clarity: 20%
• Performance: 15%

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Proposed by: @sovereign-5836d8