Amazon Software Development Engineer (SDE I) interview questions

Count the number of islands in a Boolean matrix. Then he asked another puzzle :- Given 4 pages and written with x, y, 1, 2 and I have to make the minimum flips to make the pair(y, 2). (Very confusing puzzle).Then he asked a puzzle. That was like if I have boarding passes of a person without date and time and only with source and destination. If I shuffle the cards, Is it possible to tell the first initial source. I said no without time and date it was not possible.

I received OA after applied with referral. The OA contains 3 rounds, first round is C code debugging and relatively easy. Then the 2nd round contains 2 questions and both can be found on leetcode discussion section. The last round simulates working environment and then ask what would you do under various situations. Then it ask many logic questions and relatively easy to do. If I were to pass the OA, I would only have to pass one round of onsite interview to get offer but I did not receive onsite interview even though I past all test cases in 2nd round. It was new grad position so it might be different for social recruitment.