Design an In-Memory Key-Value Store with TTL

Problem

Design an in-memory key-value store with expiry, like a mini-Redis.

Requirements

• set(key, value, ttl) / get(key) / delete(key)
• Keys expire after TTL
• Optional: getMostRecent()

What evaluators look for

• Clean separation: store, expiry policy, eviction
• Lazy vs active expiry trade-off
• Thread safety
• O(1) operations

Extension

Add LRU eviction when a memory cap is hit; discuss interaction with TTL.