Start by clarifying requirements and constraints, then outline a BFS-based crawler that tracks visited URLs, handles HTTP errors with retries and backoff, and uses dependency injection for testability. Emphasize cycle prevention, error handling, and a testing strategy with mocked HTTP responses.
Pro tip: Mention that you'd use a queue for BFS to find the shortest path and set a maximum depth or visited set size to prevent infinite loops. Also, highlight the importance of idempotency and rate limiting to avoid overwhelming servers.
Ask about expected scale, allowed concurrency, timeout limits, and whether the target string can appear in any part of the response body. Confirm if only URLs from a specific field (e.g., JSON) should be followed.
Use BFS with a queue to explore URLs level by level, ensuring the shortest path. Maintain a visited set to avoid cycles and a max depth to prevent infinite loops.
Implement retry logic with exponential backoff for transient errors like 503s. Distinguish between retryable (5xx, timeouts) and non-retryable (4xx) errors, and consider circuit breakers for repeated failures.
Abstract HTTP calls behind an interface and inject a mock client in tests. Use a local test server or mock responses to simulate various scenarios: success, errors, cycles, and the target string.
Mention trade-offs between BFS and DFS, concurrency vs. simplicity, and memory usage of visited set. Suggest optimizations like caching, rate limiting, and using a bloom filter for large-scale visited tracking.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.