I submitted my resume online and was connected by a recruiter. Then, I scheduled two 45-minute technical phone interviews with Google engineers. The interviews were not hard, but I gave them a wrong answer about time complexity. However, the engineers were very nice and friendly.

After that, I received an email about a third phone interview. I believe this might have been because I performed just average in the first two rounds, and they wanted to give me another chance. However, later I had several other offer deadlines approaching and thus declined the further interview process with Google.

Google's host matching round takes quite some time, but it's a great company nonetheless.

Not so hard. They like to ask complexity analysis for each question.