LeetLLM
MediumCachingPython 3

LRU TTL Cache

Combine recency ordering and TTL cleanup without corrupting cache invariants.

35m3 sample tests5 hidden tests

Implement a bounded cache with least-recently-used eviction and optional TTLs.

Requirements

  • Define LRUTTLCache(capacity, now).
  • put(key, value, ttl=None) stores a value.
  • get(key) returns the value or None when missing or expired.
  • get marks a key as most recently used.
  • When capacity is exceeded, evict expired entries first, then least recently used entries.
  • Expiry is inclusive: a key is expired when now() >= expires_at.

Example

python
1cache = LRUTTLCache(capacity=2, now=lambda: 0) 2cache.put("a", 1) 3cache.put("b", 2) 4assert cache.get("a") == 1 5cache.put("c", 3) 6assert cache.get("b") is None

Constraints

  • Use standard-library Python only.
  • Don't use functools.lru_cache.

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