There isn't much Adyen interview experience on the forum, so let me contribute mine.
I'd never heard of Adyen and didn't even know they hire in the US — they have an office in Chicago and require onsite for a few days.
Interview process: HR -> HackerRank OA -> Technical -> System Design -> Leadership -> Board
The OA had two questions: the first was LRU, the second was similar to combination sum, but both had a bank-transfer backstory.
I passed the OA tests 100%, but according to HR, passing all the tests doesn't necessarily mean you pass this round — they want to look at the code itself.
The Technical round was about explaining how I solved those two questions, plus my past work experience.
I thought it would just be a formality — I'd already written out the solutions, and with 10 years of Java engineering under my belt, of course I'd pass. I was also in the middle of prepping a project deep dive for another company and had drawn a really nice diagram I could show off. I actually planned to cancel even if I advanced to the next round, since I already had an offer from somewhere else — and then I got rejected.
The two people interviewing me: one was a TL who had come over from the Netherlands and had been there many years; the other interviewer had been there four years and kept a poker face the whole time.
They asked very detailed questions. For my LRU I'd written my own doubly linked list, and I explained why I didn't use Java's LinkedList, and explained that you could actually use a LinkedHashMap instead. They asked about multithreading and how it would work in production, and I brought up Redis.
For the second question I used backtracking, analyzed the complexity, and since I said all the tests passed, I ended the OA half an hour early without thinking there might be a better algorithm (I shouldn't have said that — too relaxed). So they asked how I'd do backtracking, and I said it's basically walking the tree with pruning. They asked about concurrency — what if the API gets called a lot of times — and I talked about optimizing with a shared list.
I felt like I answered well, but I still got rejected. HR gave me feedback. (HR was actually pretty professional about the whole thing — I went back to China for a month in the middle of this, and HR sent the OA right on schedule as I was about to fly back to the US. I asked if I could push it back two weeks for jet lag, and they said yes.)
My LRU explanation was okay, but I didn't go into detail — like the dummy node (they didn't even ask about that?) — and I struggled to explain why I used backtracking.
Concurrency wasn't good.
My overall project explanation was okay, but I struggled to explain my individual contribution.
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