I had two back-to-back phone interviews.

The first was harder due to communication issues. I couldn't understand the interviewer properly because of his accent.

The second interview was fine. There were no questions I didn't expect, and the interviewer was helpful in answering my questions.

I passed the interview stages and entered the matching stage very early on. However, I waited months for the first match and did not get picked for that project. Finally, I was denied the internship due to a lack of match.

I would say that the interviews were not extremely hard. If you prepared, then there should be no problem. The matching stage is really the issue. If you're lucky, you get matched early on. If not, you can wait for months and not get a match.

There's an array filled with characters and numbers, along with spaces. Each index contains only one ASCII character or a space. Give an algorithm that moves all spaces to the end or beginning of the array, while keeping the rest of the characters in their original chronological order. This can be done in O(n).