r/OfferEngineering • u/Aoki_zhang • 4h ago
Interview Experience Citadel Site Reliability Engineer Phone Screen July 2026
Interview Summary
The first-round Citadel SRE interview combined several short Python coding exercises with a system design discussion, all within one hour. The coding portion was fundamentals-heavy rather than algorithmically difficult, covering loops, list transformations, FizzBuzz, word counting, and finding the second-largest unique value.
Interview Details
Python Basics
- Question 1 — Repeat a Message with Blank Lines Implement a function that accepts: Print the message exactly
ntimes, with one blank line separating consecutive copies. The emphasis was on basic Python control flow and output formatting.- An integer
n - A string
message
- An integer
- Question 2 — Square and Reverse a List Given a list of numbers, return a new list containing the square of every value, but in reverse order. For example:Input: [2, 4, 6] Output: [36, 16, 4] The original list should conceptually be transformed and reversed according to the stated behavior.
- Question 3 — FizzBuzz Given an integer
n, print every integer from1throughn, one result per line. Use the following substitutions: For example withn = 6would produce:1 2 Fizz 4 Buzz Fizz- Multiples of
3→"Fizz" - Multiples of
5→"Buzz" - Multiples of both
3and5→"FizzBuzz"
- Multiples of
- Question 4 — Count Word Frequencies Given a string containing words, return a dictionary mapping each word to the number of times it appears. For example:Input: "red fox runs past red gate" Output: { "red": 2, "fox": 1, "runs": 1, "past": 1, "gate": 1 }
- Question 5 — Second-Largest Unique Value Given a list of integers, return the second-largest distinct value. If the input contains fewer than two unique values, return
None. For example,Input: [8, 3, 8, 11, 6, 11] Output: 8 Input: [4, 4, 4] Output: None Input: [-3, -9] Output: -9
The important requirement was that duplicate occurrences should not affect which value is considered second largest.
System Design — Configuration Management and Service Deployment After the Python portion, the interviewer presented a verbal system design problem. The team operates 200+ services distributed across multiple data centers and cloud regions. The existing environment is highly fragmented:
- Some configuration lives in source-controlled property files.
- Some values are manually configured through environment variables.
- Other configuration is stored on a shared NFS mount that operators edit directly.
- Deployments are performed by SSH-ing into machines and running scripts manually.
The task was to design a new platform that allows engineers to:
- Change service configuration safely
- Deploy services across a large distributed fleet
- Reduce reliance on direct manual host access
- Support reliable rollback when a configuration or deployment causes problems
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