# Amazon interview experience | Set 398 (On-Campus)

The online round was hosted in HackerEarth platform. It had 20 MCQ’s of 1 mark each and 0.25 negative mark and 2 coding questions of 10 marks each. The MCQ’s was mostly from Data Structures and Operating Systems, and few questions from networking, DBMS and 1 Java question.

After clearing online round there were 3 technical round and 1 bar raiser round.

Resume was taken before interviews.

Round 1:

In this round, the interviewer asked about my coding and scholastic achievement.

1. Favorite subject and questions on that topics.

2. Basic question on space and time complexity

3. Write a program to print all permutations of given string and discuss its working as well as space and time complexity in detail. https://www.geeksforgeeks.org/write-a-c-program-to-print-all-permutations-of-a-given-string/.

4. Write a program to find number of shapes in Boolean matrix. https://www.geeksforgeeks.org/find-number-of-islands/.  He asked me about time complexity and space complexity. At the beginning space complexity of my solution was O(mn). I presented 4 methods and reduced its complexity to O(1). I solved it by both dfs and bfs.

Round 2:

In this round, the interviewer asked me to introduce myself and short discussion on my resume project

1. Write a program for Lowest Common Ancestor in a Binary Tree. https://www.geeksforgeeks.org/lowest-common-ancestor-binary-tree-set-1/.

2. Write programs for Fractional Knapsack and 0/1 knapsack code of recursive solution and its optimization (concept of dynamic programming). https://www.geeksforgeeks.org/knapsack-problem/.

3. Write a program and approach for Minimum no. of iterations to pass information to all nodes in the tree. https://www.geeksforgeeks.org/minimum-iterations-pass-information-nodes-tree/. I was very close to the solution and he was very impressed by my approach of recursion. He interrupted me between the solution and asked further questions.

4. Approach for K smallest element in array. https://www.geeksforgeeks.org/k-largestor-smallest-elements-in-an-array/. I presented 3 solutions and heap solution then he asked me about heap and its time and space complexity.

5. Approach for Largest Rectangle in Histogram. https://www.geeksforgeeks.org/largest-rectangular-area-in-a-histogram-set-1/. I presented two solutions naïve solution and stack based solution.

Round 3:

In this round, the interviewer asked me about my resume project and deep discussion on my projects.

1. Write a program to find position of an element in a sorted array of infinite numbers. https://www.geeksforgeeks.org/find-position-element-sorted-array-infinite-numbers/. I presented 3 solutions in most optimized way.

2. Question on computer science fundamentals. Detailed explanation of virtual memory, paging page faults etc.

3. Write a program for Minimum Number of Platforms Required for a Railway/Bus Station. https://www.geeksforgeeks.org/minimum-number-platforms-required-railwaybus-station/.

4. Write a program to count set bit of a number. https://www.geeksforgeeks.org/count-set-bits-in-an-integer/. I presented 3 solutions and he was impressed by my last solution of using concept of last bit set using formula x&-x.

5. Last question similar to the concept of this question sort numbers stored in different machines. https://www.geeksforgeeks.org/sort-numbers-stored-on-different-machines/.

Round 4:

This round was based on designing problems.

Min Cash flow among friends. https://www.geeksforgeeks.org/minimize-cash-flow-among-given-set-friends-borrowed-money/. I solved by n^2 and nlogn complexity. In nlogn I used the concept of heap.

In each round interviewers were giving test cases to run on the programs and expecting very neat and clean code.

So I would recommend to have experience of competitive coding for depth knowledge of code and then follow geeksforgeeks. It has all the problems.

Before 2-3 of campus recruitment I would recommend to solve all problems of interviewbit with the help of geeksforgeeks.

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