Citadel Coding Interview Questions

Showing 5 problems of 25

• #20easyfrequently asked

  20. Valid Parentheses

  Citadel asks Valid Parentheses to test stack discipline. In financial systems, bracket-matching logic underpins expression parsers for formula engines, query validators, and order-instruction parsing — getting the stack mechanics exactly right under all edge cases matters.

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• #21easyfrequently asked

  21. Merge Two Sorted Lists

  Merging two sorted lists is the inner loop of merge sort and a primitive in time-series data fusion. At Citadel, this maps directly to merging two ordered streams of market events from separate exchanges. Interviewers watch whether you use a dummy head node and whether you handle leftover tails cleanly.

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• #53easyfrequently asked

  53. Maximum Subarray

  Kadane's algorithm is a staple in quantitative finance: finding the highest-return contiguous window in a P&L series, identifying the best momentum run in a price series, or detecting the worst drawdown period (negate the array). Citadel interviewers expect you to name the algorithm, prove it greedy, and know the divide-and-conquer alternative.

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• #70easyfrequently asked

  70. Climbing Stairs

  Climbing Stairs is Citadel's entry point for dynamic programming. The interviewer is checking whether you recognize the Fibonacci recurrence, state the subproblem clearly, and then optimize space from O(n) to O(1). Expect the question to pivot toward probability: 'What if each step choice is made with probability p?'

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• #206easyfrequently asked

  206. Reverse Linked List

  Citadel uses Reverse Linked List to probe pointer fluency. Linked-list structures appear in lock-free queues, custom memory allocators, and order-book implementations. Getting pointer reassignment exactly right — and knowing when to use iterative versus recursive — demonstrates the low-level discipline Citadel expects.

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