Citadel is a fintech company that many science and engineering students dream of, especially its Quant and Software Engineer positions, which have high salaries, hardcore technology, and difficult questions. This article organizes Citadel OA real experience + three mock questions review, suitable for students who are ready to submit the collection.
Introduction to the Interview Process
OA at Citadel is generally conducted by the CodeSignal or HackerRank platforms, and is generally more on the LeetCode Hard difficulty.
Question Coverage:
- Algorithms + Data Structures (HF: heap, greedy, double pointer, interval handling)
- Mathematical modeling (portfolio / simulated trading behavior)
- String and Matrix Handling (looks simple, but stuck at the border)
OA Question Review
Q1. Task Scheduling with Limited Threads
Question:
You are given a set of tasks, each of which has a startTime and a endTime indicating that it can only be executed within that time interval. You have k threads that can execute the tasks in parallel. Ask how many tasks can be completed at most?
Input Example:
tasks = [[1, 4], [2, 6], [4, 7], [5, 8]]
k = 2
Output:
3Q2. Profit Maximization with Transaction Cooldown
Question:
Given an array of stock prices prices, each buy must be separated by at least one day before it can be sold, and after it is sold it must be waited for one day before it can be bought again (cooldown 1 day). Find the maximum profit.
Input Example:
prices = [1, 2, 3, 0, 2]
Output:
3Problem Solving Ideas:
Three states are designed: Hold / Cool / Empty, which are realized by the state transfer equation DP.
Q3. String Mutation Validation
Question:
Given two strings s1 and s2, determine whether s1 can be turned into s2 by the following operations: each operation can replace a segment of consecutive characters with another character (unlimited segment length), unlimited number of operations.
Input Example:
s1 = "aabbcc"
s2 = "xyzxyz"
Output:
TrueProblem Solving Ideas:
Divide the string into chunks, keep the character mapping consistent between corresponding chunks, and check the mapping relationship of each segment.
High Frequency Stops & Suggestions for Passing the Levels
- Highly time-pressured: Proficiency in heap, state machine DP, and interval processing is recommended.
- Limited debugging window: Platforms do not have full logs, logic must be written correctly at once.
- Code style: clear variable names + appropriate comments.
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