Amazon Software Developer Internship interview questions

I had just three days to prepare for this round and truly speaking, it was my first experience of appearing in any such interview. This round lasted for almost 60 minutes. It began with my general introduction followed by a brief discussion on my projects. After this, the interviewer asked me four questions. Question 1:Given an array of numbers find all such triplets that satisfy the given condition.Condition: a[i] < a[j] < a[k] where I < j < k. At first go I thought that it was a pretty easy question but slowly the mist started to clear and I realized how tough it was. The interviewer wanted me to solve it in linear time i.e. O(N) Question 2:Given two trees check if they are mirror images of each other or not. This was a straight forward question and it took me less than 10 minutes to code it. Now the interviewer wanted to test my understanding of operating systems and asked two fairly direct questions, to which I gave my answer based on my understanding (not bookish definition as I did not remember any of those). Question 3 & 4:What is semaphore and what do you mean by a deadlock.

Course Schedule II from Leetcode