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LRU cache with capacity eviction

seniorjava · AI-on
  1. 1Restate the problem in one line
  2. 2Sketch the data model yourself
  3. 3Ask AI for a skeleton ONLY
  4. 4Ask AI for a test plan ONLY
  5. 5Implement the core logic yourself
  6. 6Run the tests — verify, don't trust
  7. 7Ask AI for edge cases you missed
  8. 8Ask AI to review your code
  9. 9Make the final judgment yourself

Problem

Implement a fixed-capacity LRU cache of int keys to int values. get(key) returns the value or -1 if absent and counts as a use. put(key, value) inserts or updates; when the cache is over capacity, evict the least-recently-used key. Both get and put must keep the most recently touched key safe from the next eviction.

iThe deal with the pair partner

The AI is deliberately fallible — it gives hints, not solutions, and sometimes proposes wrong code. It cannot touch your editor. Paste what you choose, then Run. Anything AI-derived stays UNVERIFIED until your tests go green.

Self-check

  • ☐get on a missing key returns -1 and does not insert anything
  • ☐get refreshes recency so a just-read key survives the next eviction
  • ☐put on an existing key updates the value without growing the size
  • ☐eviction removes the least-recently-used key, not the oldest-inserted one
  • ☐you stated the per-operation complexity you are aiming for (O(1) is the goal)
Hints / what this doesn't test

This is an Opendoor-flavored applied problem: a small stateful component with an eviction policy, not a puzzle. Restate it before coding — "So get is a use that makes a key recent, put can overflow, and the thing I drop is the least-recently used entry — reads count, not just writes?"

What this problem does not test (say so out loud): thread safety, an access-ordered LinkedHashMap(.., true) with removeEldestEntry (a valid shortcut worth naming), TTL/time-based expiry, and generic key/value types are out of scope here — but a senior names that the get-refreshes-recency rule is the part most naive caches get wrong.

Solution.javaauto-runs ~0.8s after you pause
unverifiedEdited since last clean run — run to verify.

Tests

○ Not run yet — edit the code or press Run
  • ○hit
  • ○miss
  • ○evict_lru
  • ○kept_recent
  • + 2 hidden tests — revealed once the visible ones pass

Pair partner (병신 모드 · 버그 잡기)

gpt-4o-mini

Ask for a skeleton or a test plan — not the answer. Then implement the core yourself and come back for edge cases. Remember: the partner is fallible. Verify everything by running it.

The partner sees your editor but cannot change it. Copy any suggestion in by hand, then Run to verify.

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