Recruiter Screen - 30 mins

Recruiter was super nice. Talked about all things Wise. The work, the culture, future projects etc.

Some technical questions:

1. What is the difference between process and thread
2. When will you use process vs thread
3. Difference between optimistic and pessimistic locking
4. How to avoid charging twice in payment APIs
5. What is deadlock

Pair Programming

NxN tic tac toe with wincount given, if no of consecutive Os or Xs in a line equals "wincount" then the player wins. Write the win condition logic.
The interviewer was very nice and supportive. Eventhough this was an easy question, I got confused with the matrix math for diagonals and could not complete the question.

I thought I would be rejected but they asked me to appear for the next round.

(This is a known Wise question but I had forgotten to practice it. Wise does not ask LC style questions so it's good to practice all previously asked.)

System Design

Buy 10 Million Wise Stock

Wise wants to raise money by selling some of the company's stocks to its own customers, similar to a "crowdfunding" event.
Wise plans on raising £100 million by selling 10,000,000 of the company's shares, each worth £10 (the value of each share is fixed).
Wise customers will have the chance to login to the app/website and buy a selected number of shares using the money they have in their Wise account.
Each customer has a record of their funds stored in the "Balance Service" which is the source of truth for transactions that affect customers' accounts. The "Balance Service" is used to deposit and withdraw money from customers' accounts.
Design a system that lets users buy a selected number of shares using the money in their Wise accounts, during a limited amount of time (1 week).
We expect a high amount of concurrent users (e.g. 5 million), so the load generated by the crowdfunding event should not degrade other services offered by Wise that rely on "Balance Service" (e.g. withdrawing money to fund payments)

This is a popular question for Wise and I had prepared for it but I still fumbled it. Badly. I had all the answers for contention, scale etc but my delivery was very haphazard and the interviewer had to ask specific questions to ensure all relevant topics were covered.

After this, I was ghosted. As expected.

I felt really bad for wasting this opportunity and fumbling a process which was so reasonable and much easier than FAANG+ which have 6 rounds with crazy expectations.