Wise | SSE | London | Nov 2025 | Rejected
Summary
I interviewed for a Senior Software Engineer position at Wise in London and was rejected after the System Design round. The process included a recruiter screen, a pair programming session, and a system design interview.
Full Experience
My interview journey at Wise for a Senior Software Engineer role started with a 30-minute recruiter screen. The recruiter was incredibly pleasant and provided a comprehensive overview of Wise's work, culture, and upcoming projects. This round also involved some technical questions.
Next, I moved on to a pair programming session. The task was to implement the win condition logic for an NxN Tic-Tac-Toe game, where a player wins if they achieve 'wincount' consecutive 'O's or 'X's. Despite the interviewer being very nice and supportive, I found myself getting confused with the matrix math required for diagonals and, regrettably, couldn't complete the question. Even though I considered it an easy problem, I struggled. Surprisingly, I was still asked to proceed to the next round.
The final stage was a System Design interview. The problem presented was to design a system for Wise's 'crowdfunding' event, aiming to sell 10,000,000 shares worth £10 each to customers, raising £100 million. Customers would use their existing Wise account balance, with the 'Balance Service' acting as the source of truth. The system needed to operate for a limited period (1 week) and handle a high volume of concurrent users (e.g., 5 million) without negatively impacting other Wise services relying on the 'Balance Service'. This was a well-known Wise question that I had specifically prepared for, but I fumbled my explanation badly. While I had the necessary points about contention and scaling, my delivery was disorganized, and the interviewer had to prompt me with specific questions to ensure all relevant topics were covered. After this round, I was ghosted, which I had anticipated given my performance. I felt a great deal of disappointment for not capitalizing on an opportunity that seemed more reasonable and less demanding than the typical FAANG+ interview processes.
Interview Questions (7)
Explain the fundamental differences between a process and a thread.
Describe scenarios where you would prefer to use a process over a thread, and vice-versa.
Explain the differences between optimistic and pessimistic locking mechanisms.
Discuss strategies and techniques to prevent duplicate charges in payment API integrations.
Define what a deadlock is in concurrent systems.
Implement the win condition logic for an NxN Tic-Tac-Toe game where a player wins if they have 'wincount' consecutive 'O's or 'X's in a row, column, or diagonal.
Design a system for Wise's crowdfunding event to sell 10,000,000 shares (each worth £10) to its customers, aiming to raise £100 million. Key requirements:
- Customers can buy shares using funds from their Wise account via the app/website.
- The "Balance Service" is the source of truth for customer funds.
- The event is limited to one week.
- The system must handle high concurrency (e.g., 5 million users) without degrading other services that rely on "Balance Service" (e.g., withdrawing money for payments).
Preparation Tips
I knew the System Design question was popular for Wise and had prepared for it. For the Pair Programming round, I acknowledged that it was a known Wise question that I had forgotten to practice, noting that Wise tends not to ask typical LeetCode-style questions. It's good to practice all previously asked questions for Wise.