Fourteen public candidate reports, plus the current 2026 on-campus test invite.

For Momo.

Coverage: SWE intern, new grad, Python, and senior software roles; OA, phone, and onsite rounds; mostly U.S. reports from April 2019 to September 2026. One Quant Trader coding question is kept in a separate note and is not part of the 14 SWE reports.

Not done yet! There will be one more update and I am very sure there will be more OA questions in that update.

The short version

The main thing to know: this is not just a LeetCode interview. Old Mission also cares about what happens under the hood.

1. The current first round is on paper. The 2026 invite says it is a 50-minute proctored test on campus. If you pass, interviews happen on campus the next day.
2. Study real CS basics. Candidates mention operating systems, Linux, C++, Python, data structures, algorithms, and short code snippets.
3. Know memory well. Stack vs. heap, allocation, move semantics, and low-level C++ all showed up in firsthand reports.
4. The coding can take different forms. Reported tasks include a Restricted JSON Parser, Merging Palindromes, an unordered-map implementation, and a small OOP task built around shopping CSV files.
5. Python roles are different. One candidate got detailed Python multiple choice, basic Linux questions, and an OOP exercise. Another was told to expect Python DSA, analysis, and Linux.
6. The process can move fast after the test. Reports include recruiter calls, short technical screens, live coding, two onsite coding rounds, and chats with the CTO or CEO.
7. Old reports are not a blueprint for 2026. Candidates saw Codility in 2022, HackerRank in 2024, online C++ coding in 2025, and an in-person test in 2026.

A simple prep plan: start with CS fundamentals, review C++ or Python carefully, practice Linux, then solve one coding problem on paper and explain every choice you make.

The 2026 on-campus test

OA 01: What the invite says

Format: On campus · Time: 50 minutes

1. The first round is a proctored paper test.
2. Candidates who pass come back for in-person interviews the next day.
3. The invite does not say how many questions there are, which language is used, or what score is needed.

So follow your own invite. Do not assume the old Codility or HackerRank format still applies.

OA 02: What two recent candidates saw

Report dates: August and September 2026 · Roles: SWE Intern and Software Development Engineer

1. One candidate got a paper test on CS fundamentals. The one question they remembered was the difference between stack and heap allocation.
2. Another candidate described an in-person test with low-level programming questions, especially C++.
3. Both called the test difficult and both reported no offer.

That is useful direction, but it is not the full paper.

How the OA changed over time

OA 03: The knowledge section

Older reports overlap on the same broad areas:

1. Operating systems and core CS.
2. Linux commands and shell basics.
3. C++ and Python behavior, sometimes shown as short code snippets.
4. Data structures, algorithms, graphs, and complexity.
5. One 2024 HackerRank also included probability and information theory.

The size changed by year. Two candidates in 2022 remembered about 30 multiple-choice questions and two coding problems. A Python candidate in 2025 reported 50 Python questions, 15 Linux questions, and one coding problem.

OA 04: The platform changed too

1. Two 2022 candidates used Codility.
2. A 2024 Software Developer candidate used HackerRank.
3. A May 2025 candidate got one online C++ problem.
4. The current 2026 process is an in-person paper test.

There is no single old OA format you can safely memorize.

Reported topics and tasks

C++ and systems

1. Explain stack memory vs. heap memory.
2. Answer low-level C++ questions. The candidate did not remember the exact wording.
3. Work through C++ memory-allocation questions in a one-hour C++ and Linux quiz.
4. Explain move semantics.
5. Answer OS questions quickly and explain the ideas out loud.
6. Know basic Linux commands such as grep, pipes, and permissions.

Coding and OOP

1. Restricted JSON Parser. One candidate had to use C++ and parse a limited form of JSON. The public report does not give every grammar or error rule.
2. Merging Palindromes. A 2024 HackerRank candidate named this as one of two coding questions. They did not share the full statement.
3. Implement an Unordered Map. A senior candidate had to build an unordered_map-style class in C++ during a phone screen.
4. Shopping CSV class. A Python candidate worked in a prepared Linux container and designed a class for shopping data spread across several CSV files. The report does not give the file columns, methods, or output.
5. Regular coding problems. Reports range from two easy-to-medium questions to one LeetCode-hard problem with one hour and no test cases.

Python

1. Explain static methods.
2. Be ready for detailed questions about Python behavior.
3. For a Python SWE role, one candidate was told the next stage would include Python DSA, a Python analysis task, and a Linux challenge.

One useful but separate data point

A 2024 Quant Trader candidate got a running-median problem: return the median after each growing prefix of a list, up to a given position. It is good heap practice, but it came from a different role and the report did not explain how to handle an even number of values. I would not call it a confirmed SWE question.

What I left out

A few prep pages claim Old Mission asks candidates to build a deque, an allocator, or a lazy singleton. I could not find the original candidate reports behind those claims, so I did not count them as real questions. Recent Reddit posts about the 2026 campus test were also written before the candidates took it.

14 candidate timelines

01: Paper test and stack vs. heap

Report date: September 9, 2026 · Role: SWE Intern · Result: No offer

1. In-person paper test on CS fundamentals.
2. One remembered question: what is the difference between stack and heap allocation?
3. The candidate felt the test covered material that many normal classes do not spend much time on.

The rest of the paper was not shared.

02: In-person low-level C++ test

Report date: August 4, 2026 · Role: Software Development Engineer · Result: No offer

1. The first round was in person.
2. It went deep into programming-language details.
3. The candidate only described the questions as low-level C++.

03: Python screen, then DSA and Linux

Report date: July 13, 2026 · Interview date: June 2026 · Role: Python Software Engineer · Location: Chicago · Result: No offer

1. Applied online and later spoke with a senior software engineer.
2. One question asked what static methods are in Python.
3. The next stage was supposed to include Python DSA, a Python analysis task, and a Linux challenge.

The candidate did not share those later tasks.

04: Five-stage Software Developer loop

Report date: April 16, 2026 · Role: Software Developer · Result: No offer

1. OA with CS trivia and LeetCode-style coding.
2. Recruiter call.
3. A fast 15-minute CS quiz.
4. LeetCode phone screen.
5. Onsite coding and behavioral interviews, plus a conversation with the CEO about past experience.

That was one candidate's loop. It may not match every team.

05: A 15-minute OS blitz

Report date: September 29, 2025 · Role: Software Engineer · Location: Chicago · Result: No offer

1. First came a 30-minute recruiter call.
2. Then a 15-minute phone screen.
3. The engineer moved quickly through standard OS questions and asked the candidate to explain the ideas.

No exact OS questions were saved.

06: C++ JSON parser

Report date: May 12, 2025 · Role: Software Engineer · Result: No offer

1. One online coding problem.
2. C++ was required.
3. The task was a Restricted JSON Parser with a limited JSON format.
4. The candidate thought LeetCode medium and hard practice was the closest preparation.

The source does not include the complete grammar, so the linked practice problem states its own rules clearly.

07: New-grad virtual and onsite rounds

Report date: April 4, 2025 · Role: New Grad SWE · Result: Declined offer

1. OA.
2. Recruiter screen that went back over some OA questions.
3. One 45-minute virtual technical interview.
4. Two 45-minute onsite technical interviews.
5. Behavioral chat with the CTO.

The candidate shared the structure, not the coding questions.

08: Python quiz, Linux quiz, and a CSV class

Report date: February 8, 2025 · Interview date: December 2024 · Role: Python Developer · Location: Chicago · Result: No offer

Online test

1. Fifty Python multiple-choice questions.
2. Fifteen basic Linux questions, including grep, permissions, and pipes.
3. One LeetCode-style problem that felt medium.

Live coding

1. The candidate worked inside a Linux container prepared by the interviewer.
2. The task was to design a class for shopping data stored in several CSV files.
3. It was an OOP exercise, not a standard LeetCode problem.

This is a strong lead, but there is not enough public detail to rebuild the exact task.

09: One hour of C++ and Linux questions

Report date: February 4, 2025 · Role: Software Engineer · Result: No offer

1. One-hour multiple-choice test.
2. Topics included C++ and Linux.
3. The only exact area the candidate remembered was C++ memory allocation.

10: HackerRank with two coding questions

Report date: March 14, 2024 · Role: Software Developer · Location: New York · Result: No offer

1. HackerRank assessment.
2. Multiple choice on probability, graph theory, C++, Python, information theory, and algorithms.
3. Two coding questions.
4. One of them was Merging Palindromes.

The second coding question was not shared.

11: Senior SWE — Linux, C++ library work, and unordered_map

Report date: December 13, 2022 · Interview date: October 2021 · Role: Senior Software Engineer · Location: Chicago · Result: No offer

Online test

1. One LeetCode-hard problem.
2. One hour.
3. No test cases were provided.

Phone screen 1

1. Linux fundamentals.
2. Add a feature to a C++ library from the Linux command line.

Phone screen 2

1. Implement an Unordered Map in C++.
2. The candidate ran into several implementation bugs and did not move on.

This was a senior interview in 2021, so use it as a depth check, not as a prediction of the current intern test.

12: 2022 OA focused on DSA

Report date: August 2022 · Role: New Grad SWE

1. About 30 multiple-choice questions, mostly data structures and algorithms.
2. Two coding questions.
3. The candidate's main advice was simple: watch the clock.

The coding questions were not shared.

13: 2022 Codility focused on systems and languages

Report date: August 2022 · Role: New Grad SWE · Result: No offer

1. Thirty multiple-choice questions on OS, Linux, Python, and C++.
2. Two LeetCode-style questions, described as easy to medium.
3. The candidate felt the coding was manageable and thought the quiz may have caused the rejection.

This came from a different candidate in the same recruiting season as report 12. The format matches, but each person remembered a different mix of topics.

14: Old internship report and move semantics

Report date: April 22, 2019 · Role: Software Engineer Intern · Result: No offer

1. Online coding test.
2. Phone call with the lead engineer.
3. Final round in Chicago.
4. One remembered topic: move semantics.

It is old, but it fits the same C++ depth seen in newer reports.

What repeated often enough to prioritize

Tier 1: Know these cold

1. Stack vs. heap, allocation, object lifetime, copying, and moving.
2. OS basics and everyday Linux commands.
3. Timed coding with arrays, strings, hash tables, heaps, and graphs.
4. Explaining your answer clearly, including edge cases.

Tier 2: Be ready to go deeper

1. How a hash table works: collisions, resizing, and complexity.
2. C++ container and memory tradeoffs.
3. Python methods and OOP if you are on the Python track.
4. Parser design: nested values, validation, escapes, and bad input.

Tier 3: Interview habits

1. If a prompt is vague, say what you are assuming before you code.
2. Test your own work when no examples or hidden-test feedback are available.
3. Have two or three short project stories ready for senior interviewers.

Final checklist

Paper test

☐ Explain stack vs. heap, ownership, lifetime, and move semantics without notes.

☐ Review processes, threads, virtual memory, and synchronization.

☐ Trace short C++ and Python snippets by hand.

☐ Solve one full coding problem on paper in 50 minutes.

C++ and Linux

☐ Implement an Unordered Map and explain every design choice.

☐ Review RAII, smart pointers, copy/move operations, and common undefined behavior.

☐ Practice grep, pipes, permissions, files, and processes.

Coding and design

☐ Solve the Restricted JSON Parser and test bad and nested input.

☐ Practice Merging Palindromes, then try a small OOP data task with unclear requirements.

☐ Test empty input, one item, duplicates, malformed input, and large input.

Interview day

☐ Follow your current invite, not an old platform guide.

☐ Explain assumptions, complexity, and test cases as you work.

☐ Keep your project stories short and specific.

Good luck!