Giving back to the community! Recently did the OA for Amazon. I prepped by using this post

Flight Media - basically two sums, but you had to account for multiple pairs that could add up to the target
Subscriber Groups - similar to https://leetcode.com/problems/number-of-provinces/, find the number of unique friend groups
Each question followed up with an explanation on approach and complexity. This was done on Hackerrank.

I scheduled my onsite and will share my experience once I do it. In the meantime, if anyone could share any tips or posts for onsite that would be great :)