45 min initial coding.

Onsite:

• 2 coding rounds
• 2 system design rounds
• 1 behavioral round

To prep:

Design

1. System design primer. Especially, it's important to memorize some latency numbers posted here for staff and higher levels. Candidates are expected to do back-of-envelope calculations accurately based on these numbers.
2. Systems interview course. This is not free, but offers good content. Feel free to go through the free chapters first. You can buy it if you like the free chapters.
3. Educative course. This is also not free, but provides a somewhat useful template to answer common system design questions.

Coding

This is just more practice. Buy Leetcode premium. You can sort and find out 'frequently asked questions' at Facebook, Google, Amazon, Netflix, Twitter, Apple, etc. This is very accurate in my experience. You may have to solve the top 30-40 questions for each company you plan to interview.

Design regex parser to handle * and ?.