Amazon Software Development Engineer interview questions

I Applied Online and got a call for onsite interview. There was some interview event going on and so I did not have to appear for Phone interview prior to this interview. I was flied to Seattle and had four rounds of interview. All the questions were focused on Algorithms and Data Structures. Questions were 1. "Solve a maze", you have a 2D matrix with 1's as blocked and 0's as path. Find a path from one corner to another, backtracking should be allowed. 2. Prove that tree is BST. 3. Ransom note problem - prepare a note(array) from a given magazine(array). 4. Keep track of history of users of Amazon site in pairs of 3 pages that they have consecutively visited.

I was contacted by Amazon from linkedin. They want to know if I am interested to go to sydney for their hiring event. I said I can't go to sydney because I live in Brisbane and told them that my strength is in .Net and Amazon does not hire .Net programmer but she told me that it is ok. So I accepted to have the normal method of interview. We had a few emails back and forth and the lady from Amazon was quick to respond my emails (usually a few hours). First step was a coding exercise. Usually initial coding exercises are easy and are designed to see if the interviewee can write code at all. So she sent me the question and I had three hours to finish it. The question was: given an array of ints, find the sum of most common repeated number. For example {4,2,3,1,8,3} should return 3+3 = 6. I had to give two answers one with least time complexity and one with least space complexity. So I implemented the typical answers using a hashmap, or the naive one with O(1) space complexity and one extra using sort. I unit tested and documented all my code properly, also had time to write a performance test and document how to parallelize any of the algorithms. Its been a while since I sent them the answer but I received no response. The lady who was quick to reply to my emails also did not reply to my follow up email! It is really disrespectful, asking someone to sit for a test and totally ignoring him after that! Even if my code have been terrible and the guy has had a heart attack after seeing it they could tell me that sorry, we don't want to go further! It wasn't me chasing them after all. After about a week and two follow ups, I have been said that they were trying to contact me trough another email. However I scheduled a phone interview and fingers crossed on that.