Citadel Software Engineer Coding & Algorithms Interview Questions
Practice 26 real Coding & Algorithms interview questions for Software Engineer roles at Citadel.
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Perform an External Merge Sort with a Heap
Perform an External Merge Sort with a Heap Sort an integer sequence using the two phases of external merge sort: create sorted runs that fit within a ...
Top-K Largest Elements in Every Sliding Window
This question evaluates the ability to design and maintain an ordered data structure that efficiently tracks the top K largest values within a moving ...
Find the Index Range of a Target in a Sorted Array
This question evaluates a candidate's grasp of binary search and its adaptation to locate boundary positions within a sorted array. It tests the abili...
Determine order of alien alphabet
This question evaluates the ability to infer ordering constraints among characters, model dependencies from ordered examples, and reason about edge ca...
Implement array merge, round-robin scheduler, and trading simulator
This multipart problem evaluates algorithmic problem solving and systems-design competencies including in-place array manipulation, queue-based schedu...
Implement LRU/LFU cache with custom eviction
This question evaluates proficiency in cache design and data-structure implementation, focusing on eviction policies (LRU, LFU), metadata tracking for...
Compute max team size with a core interval
You are given n employees’ working-time intervals, where employee i works during the inclusive interval [startTime[i], endTime[i]]. You want to form a...
Design a token manager with lazy expiration
This question evaluates time-based data structure design and algorithmic reasoning for managing expiring items, focusing on hashing, timestamp orderin...
Return nodes on a tree diameter path
This question evaluates understanding of graph algorithms and tree properties, specifically the ability to identify and reconstruct a longest simple p...
Compute BBO and NBBO from order data
You are given a list data of order records. Each record is a 4-tuple: ` (exchange_id, price, quantity, order_type) ` - exchange_id: string/int identif...
Implement task queue with insert, delete, execute
Problem: Task manager with insert/delete/execute-next Design a data structure to manage executable tasks. Each task has: - taskId (unique) - priority ...
Optimize password transform and discount scheduling
Optimize password transform and discount scheduling Part 1 — Transform to palindromic k-periodic string: Input: a lowercase string currentPassword and...
Solve four algorithmic problems
Answer the following independent algorithmic questions: 1) Count extendable prefixes for '10' subsequences: Given a binary string s and an integer k, ...
Design dynamic weighted random sampling with updates
Problem: Support weighted random sampling with insert/delete Design a data structure that maintains a dynamic set of items, each with a positive integ...
Solve two DS&A optimization problems
Problem 1 — Maximize alternating-sum over four array partitions: Given an integer array arr[1..n] (1-based). Choose indices a, b, c with 1 ≤ a ≤ b ≤ c...
Minimize image processing cost with discount
Question You have n images. For the i-th image, processing costs filterCost[i] per day and must run from startDay[i] to endDay[i] inclusive. Each day ...
Implement a single-producer multi-consumer ring buffer
Implement a fixed-capacity ring buffer in C++ for a setting with one producer and multiple consumers. Design a class that stores integers in a preallo...
Minimize changes for k-periodic palindrome
Question Given a string currentPassword (length N) and an integer k (1 ≤ k < N, N ≤ 2·10^5, lowercase letters, N divisible by k), find the minimum num...
Find the Shortest Target-Sum Path
This question evaluates skills in binary tree traversal, path-sum computation, and optimization for selecting a root-to-leaf path with the minimal num...
Merge K timestamped lists with timestamp coalescing
This question evaluates algorithmic skills in merging multiple sorted sequences, coalescing records by key (timestamp), merging sorted value arrays, a...