Citadel / Citadel Securities Interview Question Bank
Citadel and Citadel Securities run two distinct loops sharing one brand. Citsec (the market maker) hires for HFT software, quant research and quant dev; its phone screens lean on small, sharp coding prompts (merge-K, ring buffers, stock-DP ladders) and the loop is famously single-fail — any weak round and the next interview is cancelled within a day. Citadel (the hedge fund) and its sub-orgs (GQS, EQR, NXT) lean harder on probability brainteasers, deep resume drilling and a multi-week team-match stage where coding bar drops but cultural and PM-style fit dominates the offer decision.
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practice in the online judgeContent-Deduplicating File SystemSearch Suggestions SystemMinimum Changes to Make Every Password Block a PalindromeMaximize Earnings by Converting Days OffMinimum Changes to Make Password Blocks PalindromicMaximize Earnings by Converting Days OffMinimum Character Changes for Palindromic Password BlocksMaximize Earnings by Converting Days Off to WorkdaysMinimum Changes for Block Palindrome PasswordMaximum Earnings After Converting Days OffMinimum Changes for a Palindromic Periodic PasswordMaximize Earnings by Converting Days Off to WorkdaysTask Dependency OrderingClosest Pair of Points in a 2D PlaneOnline Batched No-Intercept RegressionPiecewise Linear Interpolation with ExtrapolationTown Temperature Regression AnalysisMinimum Changes for Palindromic Length-k SubstringsMaximum Earnings After Converting Days OffCandySecond Largest Distinct ValueWord Frequency CounterFizzBuzzSquare and Reverse a ListPrint a Message Repeatedly with Blank LinesReact Real-Time Event Feed DashboardLimit Order Book Matching EngineDesign a Low-Latency Bounded Queue and Size Its CapacityImplement a C++ Task Scheduler with Parameterized TasksStatistics from a 256-Bucket Frequency Array