Everyone Counts Software Developer Intern interview questions

I was pretty lucky because I got an interview in less than a week after I emailed my resume which is not vey usual. We then scheduled an on-site interview. I was interviewed by a senior developer who was very friendly and helpful. I don't remember all the questions but overall here is how he interviewed: 1) resume, courses taken, challenges etc. He then said that he will 1st ask easy, then medium, and then hard questions. Easy: - strings, substrings example - strings vs strinbuffers vs stringbuilders Medium: - JUnit (write a tester method for some method) - try, catch, final, finally, finalize keywords Hard: - There was just one problem which I can't remember, sorry. I had only 5-10 min left, so it was really hard to solve it, but he wanted to know how I would approach this problem, which data structure, some pseudocode The length of interview was 1.20min In about 10 days I got a job offer.