I applied through the website for a UK position.

I went through a phone interview with two relatively easy questions. The interviewer was overall satisfied and said they would get back to me quickly.

They did so the same day, confirmed I passed the interview and would have a next round, and asked if I needed a visa to attend the on-site interview. I answered.

After 7 days, I received an email from HR stating they could not move forward and would have to cancel the upcoming interview. They explained they had already "extended" a lot of offers and didn't want to waste my time.

This was very unprofessional. You should not confirm something if you are unsure about it for any reason, never!

1. Find the number of times a string appears in another string.
2. Easy data structures question.