Adyen Software Engineer Interview Experience — 100% on the OA, Rejected After the Technical Round

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.