Block Software Engineer interview questions

I submitted my resume to my university's career website, after which I received an email to complete a coding challenge online. This was used to determine whether I got an on-campus interview. There were two questions, both of which I put below. I finished the first and got halfway through the second one. After that I got the on-campus interview, which was pair-coding style. We implemented a least-recently-used cache in Java. It was fun, and I was able to Google syntax I didn't know, and we ended up getting it to run. A bit later, I got an email to set up an on-site interview at Square in SF. This consisted of breakfast, three pair coding interviews, lunch, a few talks, coffee at Sightglass, and then that was it. The three questions I got were: 1. find all prime numbers under a given number 2. Fraud detection: if two merchants have swiped the same card, they are part of the same component. Find the size of the component. 3. parse TVL bytes and return cardholder name. I struggled with the last one in particular. I was notified of no offer after a week.