I was invited to this interview after doing Google Foobar.

The first-round technical interview was relatively easy. I had to code an answer to the following simple question, which I did in Python.

Then, my interviewer asked me to do the same thing with Python iterators. I wasn't sure how they worked, so he taught me how they worked. I made an implementation that didn't quite work, and we ran out of time. However, it seemed as if he didn't expect me to code it correctly due to the time constraint (the interview was going over time, as it had taken some time for me to code the first problem and he had spent some time teaching me about iterators).

My interviewer told me at the end that no one else had successfully solved that problem and that my explanation of the solution was very clear.

Then, the process was extremely slow. I'm not really sure how these interviews are evaluated, but I got a call 5 weeks later (after following up thrice) that I was rejected.

I then received an email on how to prepare for technical interviews, and the reason for my rejection didn't seem very clear. Perhaps the comments my interviewer made to Google were misinterpreted in such a way that the Google admissions people thought I had a bad interview.

For reference, I am currently in the third round of my Jane Street trading intern process, which is well-known to be far more difficult.

Code an algorithm to compress a string. For example, "ggghhef" would result in ["g", 3, "h", 2, "e", 1, "f", 1].