Design TinyURL (Encode/Decode with collision handling and optional TTL)

Problem: Implement a TinyURL encode/decode service Implement a simplified TinyURL service that encodes a long URL into a short URL and decodes it back. Requirements Implement two functions (or equivalent APIs): encode(longUrl) -> shortUrl Given a string longUrl, return a short URL shortUrl that can be mapped back to longUrl. decode(shortUrl) -> longUrl Given shortUrl, return the original longUrl. If shortUrl does not exist (or is expired), return an empty string or null (state your choice). Constraints / Edge Cases Maintain a mapping between short keys and long URLs (use an in-memory hash map for the interview; optionally explain Redis/DB persistence). The generated short URL should be reasonably short (typically a fixed-length key). Handle collisions / duplicate keys: if a generated key already exists but maps to a different long URL, you must resolve it correctly. Optional: support TTL (expiration). I/O for Local Testing (one possible format) Multiple lines of commands: ENCODE <longUrl>: output the generated shortUrl DECODE <shortUrl>: output the restored longUrl (or NULL/empty if missing) Suggested Scale Up to 1e5 operations URL length: 1 ~ 2000 Example Test Cases Basic encode/decode: ENCODE https://example.com/a/b DECODE <the short url from previous line> Encoding the same long URL twice: Either return the same short URL (idempotent) or different ones, as long as decode works consistently. Collision handling: Force the generator to produce the same key for different long URLs; ensure you don’t overwrite incorrectly. Invalid short URL: DECODE http://tiny/doesNotExist -> NULL or empty. TTL (optional): ENCODE_TTL https://a.com 1 After 2 seconds, DECODE should return NULL/empty. Example Input ENCODE https://example.com/a/b DECODE http://tiny/xxxxxx Output <line1: some short url> NULL