Prepping for these interviews is much like studying for the SATs - it's not about measuring how smart / talented you are, but how good you are at taking these tests. I say this as a primer only because rejection sucks, but knowing that it's not a dig on you personally, that it's more of a numbers game, can help you stay positive through this whole process.

I've heard a lot of success with this method:

1. Start with https://www.firecode.io/ - it's a gentler intro than most of these resources.

2. Once you can manage FireCode, move onto LeetCode as others have suggested. More specifically, the ones that have been flagged as interview problems. If you can get through the Hard ones in 30-45 min, you're good.

3. Once you feel confident in steps 1 and 2, use https://interviewing.io to take a bunch of mock interviews. The interviewers are generally from these companies, so if you do well, you'll automatically skip the phone interview and land right in the main interview space. And if you don't, no worries, you're getting practice in an interview setting, and not just in answering problems.

3b. As a supplement to #3, Google and Facebook actually hold info sessions on their interview process. My friends used those and landed at both places, respectively. They both said the info sessions were pivotal for them.

The average time my friends spent on this process was roughly 90 hours total. So if you worked on this full time for 2+ weeks, you should be prepared, or 2-3 months if you did a little bit every night while working your current job.

Best of luck!