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lru_cache.py3 bugs<br>1class LRUCache:<br>2 def __init__(self, capacity):<br>3 self.cap = capacity<br>4 self.cache = {}<br>5 self.head = Node(0, 0)<br>6 self.tail = Node(0, 0)<br>7 # ← sentinel nodes never linked<br>9 def get(self, key):<br>10 if key not in self.cache:<br>11 return -1<br>12 # ← missing MRU promotion<br>13 return self.cache[key].val
test_eviction_orderFAIL<br>expected3<br>received-1
Scenarios styled after interviews atMetaAmazonGoogleStripeShopify<br>Not affiliated with or endorsed by these companies
How a session works<br>Three stages. No hand-holding between them.<br>PickChoose a scenario<br>Select from multiple real interview formats across Easy, Medium, and Hard. Each is a broken implementation waiting to be fixed.
DebugFind and fix the bugs<br>A live test runner shows what's failing. An AI coach in the sidebar answers questions but won't write the fix for you.
ReviewGet scored on how you think<br>Six behavioral axes, an AI-generated headline about your session, and a full timeline of every decision you made.
What makes it different<br>Not LeetCode. Not flashcards. Actual interview simulation.
Debug real broken code<br>Pre-broken implementations from actual interview patterns. Find and fix the bugs, no blank-slate busywork.
AI coach, not answer machine<br>Hints redirect your thinking toward the bug. The coach refuses to write the fix and notices when you rubber-stamp its suggestions.
6-axis performance review<br>Scored on Diagnosis, Independence, Precision, Verification, Recovery, and Test Ownership. Not just pass/fail.
Real company scenario formats<br>EventEmitter (Meta), LRU Cache (Amazon), Prefix Trie (Google), Rate Limiter, Transaction Engine, and 6 more.
Hard mode<br>Adds realistic interviewer pressure: scope creep, over-engineering bait, correctness doubts. Practice staying focused.
Live in-browser test runner<br>Instant feedback on every edit. Hidden tests reveal edge cases once you complete each part.
Real problems. 3 difficulty levels.<br>Each one is a real broken implementation. A sample:<br>META● Medium<br>3 parts · 30 min<br>EventEmitter<br>Three bugs: listeners fire in reverse order, off() wipes the whole event, once() never removes itself.<br>pub-subclosures
AMAZON● Hard<br>3 parts · 35 min<br>LRU Cache<br>Sentinel nodes never linked, eviction hits the wrong end, and get/put skip MRU promotion entirely.<br>data-structureslinked list
GOOGLE● Easy<br>3 parts · 25 min<br>CSV Parser<br>Drops the last field on every row, strips leading whitespace, and enters quote mode at the wrong character.<br>parsingstrings
GOOGLE● Medium<br>3 parts · 30 min<br>Prefix Tree (Trie)<br>search() returns True for prefixes, get_words_with_prefix() builds results in reverse, case handling is inconsistent.<br>data-structuresrecursion
+ 7 more: Rate Limiter, Feature Flags, Log Query Filter, Dependency Resolver, Merge Intervals, and others.
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AI OA & Coding Interview Prep: Debug Real Code with an AI Coach