Amazon SDE-2 Interview Questions, Process, and Tips for Freshers

Round duration - 60 minutes
Round difficulty - Easy

Started with brief intro(5 mins) about interviewer.
Problem solving question, question was already there in the codelink shared by the interviewer. He explained the problem again with sample testcase. 
The Interviewer was friendly.

Q1. Course Schedule II
You have been given ‘N’ courses and some courses may have prerequisites. Now consider a matrix ‘PREREQUISITES’ of size 'M' x 2 which represents that you must complete course '...read more
Ans. Breadth-First Search
Our current algorithm is based on the idea of the BFS approach. We first process all the courses with 0 in-degree implying no prerequisite courses required. If we remove all these courses from the graph, along with their outgoing edges, we can find out the courses/nodes that should be processed next. These would again be the nodes with 0 in-degree. We can continuously do this until all the courses h...read more
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Q2. System Design
System design a live video broadcast platform.
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Round duration - 90 minutes
Round difficulty - Medium

There were 2 interviewers(India HM and Seattle HM), India HM was just shadowing and didn't ask any questions. Started with intro, he asked in detail about what I do at current company(10 mins). Again, jumped into LP's(25 mins).

Q1. Distance between two nodes of a Tree
Given a binary tree and the value of two nodes, find the distance between the given two nodes of the Binary Tree.
Distance between two nodes is defined as the minimum...read more
Ans. Naive Approach
In any rooted tree, the distance between two nodes 'U' and 'V' can be found by finding the lowest common ancestor (LCA), ‘x’ of two nodes. The lowest common ancestor (LCA) between nodes 'U' and 'V' is defined as the lowest node in the tree that has both 'U' and 'V' as descendants, where we define each node to be a descendant of itself (so if 'U' has a direct connection from 'V', 'V' is the lowest common a...read more
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Q2. Median in a stream
Given that integers are read from a data stream. Your task is to find the median of the elements read so far.
Median is the middle value in an ordered integer list. If the size of the ...read more
Ans. Brute force approach
Store the incoming data elements in a vector. Sort the vector everytime you need to output the median.
Algorithm:
1. Store the incoming elements of the data stream in a vector.
2. Step by step insert one element and sort the vector as soon as any element is added in the vector.
3. If the size of the vector is odd, print the middle element of the sorted vector.
   If the size of the vector is even, return the mean of...read more
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Round duration - 60 minutes
Round difficulty - Medium

There was only 1 interviewer in this round and We had no video sharing in this round so it was becoming difficult to understand each other.

Q1. Object Oriented Design Question
Started with brief intro about both(5 mins), then he jumped into LP's(25 mins). This was very difficult since there was no video and he was grilling me real hard on this, so...read more
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Round duration - 45 minutes
Round difficulty - Medium

This round was scheduled in the evening hours and all the participants were required to fill a form which was shared 15 minutes prior to the start of the online coding round. This form was filled out probably for the security reasons and to ensure that no one disinterested participant gives the test.

Q1. Ways To Make Coin Change
You are given an infinite supply of coins of each of denominations D = {D0, D1, D2, D3, ...... Dn-1}. You need to figure out the total number of ways W, in which you can make a cha...read more
Ans. Recursion
 
1. The idea is to use recursion.
2. For a particular coin, we have two options either include it or exclude it.
3. If we include that coin, then calculate the remaining number that we have to generate so recur for that remaining number.
4. If we exclude that coin, then recur for the same amount that we have to make.
5. Our final answer would be the total number of ways either by including or excluding.
6. There will be two edg...read more
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Q2. Validate BST
You have been given a binary tree of integers with N number of nodes. Your task is to check if that input tree is a BST (Binary Search Tree) or not.
A binary search tree (BST) is a binary tr...read more
Ans. BST property
The approach is based on the fact that the value of each node in a BST is greater than the value of all the nodes in the left subtree and smaller than the value of all the nodes in the right subtree.
 
Here is the complete algorithm-
• For each node, we store the minimum and maximum value allowed for that node. Initially, for the root node, the minimum value would be -10^9 and the maximum value should be 10...read more
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Round duration - 60 minutes
Round difficulty - Hard

This round was on call where I was just supposed to answer the tech questions that were asked. It started with a brief interview with one another and then moved to questions on DBMS, operating systems, computer networks and all. Almost 20-25 questions were asked and I probably answered 90% of them correctly.

Q1. Reverse Linked List
You are given a Singly Linked List of integers. You need to reverse the Linked List by changing the links between nodes.
Input Format :
The first line of input contains a single integ...read more
Ans. Recursive Approach
One way is to use recursion to reverse the list. Divide the linked list in two halves, the first node and the rest of the list. Reverse the second half using recursion and append the first half, that is the first node at the end of the reversed linked list. Return the head of the reversed linked list.
 
Algorithm
 
• If the list contains only one node, return the head of the list.
• Else, divide the ...read more
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Round duration - 30 minutes
Round difficulty - Hard

There was only one interviewer for this round. He continuously interacted with me and was giving me some good situational problems that were not very easy to answer. Basically those were open-minded questions which can be answered oth ways and that's why I found it quiet hard as per my nature but at the end things went well for me.

Q1. Basic Puzzles
A noticeable aspect in this puzzles is the fact that there’s a circular misplacement, which implies if apple is wrongly labelled as Apple, Apple can’t be labelled as Orange, i.e., it has to be...read more
Ans. 
Note: basically it's better if you have seen some puzzles before any HR round since they will give you an idea of what kind of problem you may encounter and then you can ace any difficult to difficult HR interview.
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Round duration - 90 minutes
Round difficulty - Easy

I got a call from an Amazon recruiter regarding the schedule of the test . She sent me the coding test link which I had to complete within a week. we can attempt the online test anytime, when we have time for a period of 90 minutes at a stretch.Once I completed the test, I got a call to schedule the interviews in two weeks.

Q1. Shopping Options
You are given the list of costs of pants in an array “pants”, shirts in an array “shirts”, shoes in an array “shoes”, and skirts in an array “skirts”. You are also given a budget amount ‘X...read more
Ans. Brute Force
We can check all possible combinations to buy items. That can be done by maintaining a variable “answer” and iterating over all four lists in a nested way such that each pant, shirt, shoe, and skirt pair can get selected and find the sum of that pair. If sum is less than or equal to budget then increment “answer” by one. Return the “answer”.

Algorithm:
 
• Create an integer “answer” equal to 0.
• First iterate ...read more
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Q2. Max Submatrix
Ninja has been given a matrix ‘MAT’ of integers having size ‘N’ x ‘M’ i.e. N rows and M columns. Ninja has to find the maximum sum submatrix in it. In other words, he has to find the maximum ...read more
Ans. Brute Force
The brute force approach is we check for every possible submatrix in the given ‘MAT’.
• 4 nested loops are required to select every submatrix of the matrix.
• 2 nested loops are required to take the sum of all the elements of the submatrix.
Here is the algorithm :
1. We declare a variable ‘MAX_SUM’ in which we store the maximum sum over all submatrices in the matrix.
2. We run a loop for ‘i’ = 0 to ‘N’:
   • We run a loop for ‘j...read more
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Round duration - 60 minutes
Round difficulty - Medium

Virtual interview occured in amazon chime.The interviewer gave his introduction, asked me a bit on the kind of projects I’ve worked on. Then he started with a data structure problem.

Q1. Clone a binary tree with random pointers.
You are given a binary tree. Apart from the left and right child pointers, each node in the given binary tree points to a random node in the given binary tree. You...read more
Ans. HashMap based approach
The idea is to use a HashMap to map the tree nodes to each clone node. We will traverse the binary tree and create a clone tree with the random pointer equal to NULL and map each node of the given tree to its clone node. Now we will again iterate through the tree and add the random pointer of each node by looking up the HashMap. 
 
The steps are as follows:
1. Let’s define a HashMap to map eac...read more
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Q2. Ninja Port
Ninja is stuck in a city with ‘N’ colonies, and each colony contains ‘K’ houses. Ninja is currently at the house number “sourceHouse” present in the colony with colony number “sourceColony”. He ...read more
Ans. Breadth First Search
We can initially create a graph with 2 nodes from each colony i.e. the first and last house of each colony would be included in the graph. We also create an edge from the node representing the last node of each colony to the node representing the first node of the next colony, and vice versa.
 
Now, we add into the graph each house that has an outgoing or incoming secret path. We also make edges ...read more
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Round duration - 75 Minutes
Round difficulty - Easy

This was taken by an engineering manager who asked me regarding my projects for around 10-15 mins and then we moved to a system design problem. He asked me to design Slack messenger.
I started by listing the functional and non-functional requirements(on which he questioned me a bit), then I moved to draw the high-level architecture. The components which I drew were the clients, gateway service(LB + authentication, etc), Messaging Service, User Service, Web Socket Manager service, Fan Out service(I added this for the group messages thing, but he didn’t interrogate much on that).

He asked me what would be the schema of my messages table and the scenarios in which the recipient user is online/offline.Also asked about the partitioning key and primary key of the 2-3 tables which I had made

Q1. Technical Questions
This was taken by an SDE III guy, who again asked me about my projects for like 10 mins and then moved on to a low level design question.He asked me to design the HackerRank platform.
Aga...read more
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Round duration - 60 minutes
Round difficulty - Hard

BarRaiser Round

This was again taken by an engineering manager who discussed my projects in depth for around 20-25 mins. In the remaining time he asked me 2 dsa questions. (Yes I too was surprised that he didn’t ask anything regarding design).

In almost all the rounds, I was asked questions related to Amazon Leadership principles, so do make sure you go through those before sitting for the interview process. You can refer to this link(https://www.codingninjas.com/codestudio/problem-lists/top-amazon-coding-interview-questions) for practicing the same, I found it useful. 
In the design rounds, interviewer doesn’t expect the most ideal answer from you and unless your choice of technology is outrageously wrong, he won’t pinpoint that.

Q1. Group Anagrams Together
You have been given an array/list of strings 'STR_LIST'. You are supposed to return the strings as groups of anagrams such that strings belonging to a particular group are a...read more
Ans. Sorting based Approach
The idea behind this approach is that two or more than two strings are anagrams if and only if their sorted strings are equal. So we will use a HashMap, let’s say “anagramGroup”, where each key is a sorted string, and the key will be mapping to the list of indices from the given list of strings that form a group of anagrams. This means that if we sort the strings at those indices, we will get the ...read more
Answered by CodingNinjas
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Q2. Add Linked Lists
Given two numbers represented by linked lists. Your task is find the sum list and return the head of the sum list.
The sum list is a linked list representation of addition of two numbers...read more
Ans. Recursive approach
One way is to recursively add the two linked lists. Keep the nodes in the recursion stack and add the last nodes first and then second last and so on. Initially, find the size of both the linked lists. If both the linked lists are of the same size, add them using recursion. Else if their sizes differ, move the head pointer of the larger linked list forward K times, where K is the difference between th...read more
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