Amazon Senior Engineer Interview Questions and Answers

Group discussion

Round duration - 60 Minutes
Round difficulty - Medium

This was a typical DS/Algo where I was asked to solve two questions related to Binary Trees and write the pseudo code for both of them followed by some theoretical questions related to Operating Systems.

Q1. 
K-th Largest Number in a BST
Given a binary search tree (BST) consisting of integers and containing 'N' nodes, your task is to find and return the K-th largest element in this BST.
If there is no K-th la...read more
Ans. 
Find the K-th largest element in a BST.
• Perform reverse in-order traversal of the BST to find the K-th largest element.

• Keep track of the count of visited nodes to determine the K-th largest element.

• Return -1 if there is no K-th largest element in the BST.
Answered by AI
Add your answer
Q2. 
Is Height Balanced Binary Tree Problem Statement
Determine if the given binary tree is height-balanced. A tree is considered height-balanced when:
1. The left subtree is balanced.
2. The right subtree is bala...read more
Ans. 
Determine if a given binary tree is height-balanced by checking if left and right subtrees are balanced and their height difference is at most 1.
• Check if the left subtree is balanced

• Check if the right subtree is balanced

• Calculate the height difference between the left and right subtrees

• Return 'True' if all conditions are met, otherwise return 'False'
Answered by AI
Add your answer
Q3. Can you explain the concepts of Zombie Process and Orphan Process in operating systems?
Ans. 
Zombie process is a terminated process that has completed execution but still has an entry in the process table. Orphan process is a process whose parent process has terminated.
• Zombie process is created when a child process completes execution but its parent process has not yet read its exit status.

• Zombie processes consume system resources and should be cleaned up by the parent process using wait() system call.

• Orphan p...read more
Answered by AI
Add your answer

Round duration - 60 Minutes
Round difficulty - Medium

This was also a Data Structures and Algorithm round where I was asked to solve 3 medium to hard level problems along with their pseudo code within 60 minutes .

Q1. 
Longest Substring Without Repeating Characters Problem Statement
Given a string S of length L, determine the length of the longest substring that contains no repeating characters.
Example:
Input:
"abac...read more
Ans. 
Find the length of the longest substring without repeating characters in a given string.
• Use a sliding window approach to keep track of the longest substring without repeating characters.

• Use a hashmap to store the index of each character in the string.

• Update the start index of the window when a repeating character is found.

• Calculate the maximum length of the window as you iterate through the string.

• Return the maximum le
Answered by AI
Add your answer
Q2. 
Problem: Search In Rotated Sorted Array
Given a sorted array that has been rotated clockwise by an unknown amount, you need to answer Q queries. Each query is represented by an integer Q[i], and you must ...read more
Ans. 
Search for integers in a rotated sorted array efficiently.
• Use binary search to efficiently search for integers in the rotated sorted array.

• Handle the rotation of the array while performing binary search.

• Return the index of the integer if found, else return -1.
Answered by AI
Add your answer
Q3. 
Count Subarrays with Sum Divisible by K
Given an array ARR and an integer K, your task is to count all subarrays whose sum is divisible by the given integer K.
Input:
The first line of input contains an...read more
Ans. 
Count subarrays with sum divisible by K in an array.
• Iterate through the array and keep track of the prefix sum modulo K.

• Use a hashmap to store the frequency of each prefix sum modulo K.

• For each prefix sum, increment the count by the frequency of (prefix sum - K) modulo K.

• Handle the case when prefix sum itself is divisible by K.

• Return the total count of subarrays with sum divisible by K.
Answered by AI
Add your answer

Round duration - 50 Minutes
Round difficulty - Medium

In this round , I was asked to code a simple question related to BST . After that I was asked the internal implementation of a Hash Map where I was supposed to design a Hash Map using any of the Hashing Algorithms that I know . This was preety challenging for me but I got to learn so much from it.

Q1. 
Ceil Value from BST Problem Statement
Given a Binary Search Tree (BST) and an integer, write a function to return the ceil value of a particular key in the BST.
The ceil of an integer is defined as the s...read more
Ans. 
Ceil value of a key in a Binary Search Tree (BST) is found by returning the smallest integer greater than or equal to the given number.
• Traverse the BST to find the closest value greater than or equal to the key.

• Compare the key with the current node value and update the ceil value accordingly.

• Recursively move to the left or right subtree based on the comparison.

• Return the ceil value once the traversal is complete.
Answered by AI
Add your answer
Q2. 
Design a Constant Time Data Structure
Create a data structure that maintains mappings between keys and values, supporting the following operations in constant time:
1. INSERT(key, value): Add or update t...read more
Ans. 
Design a constant time data structure to maintain mappings between keys and values with various operations.
• Use a hash table to achieve constant time complexity for INSERT, DELETE, SEARCH, and GET operations.

• Keep track of the number of key-value pairs for GET_SIZE operation.

• Check if the hash table is empty for IS_EMPTY operation.

• Return true or false for SEARCH operation based on key existence.

• Return the value associated...read more
Answered by AI
Add your answer

Round duration - 90 Minutes
Round difficulty - Hard

I found the online coding round of Flipkart to be quite difficult based on the constraints of the problem and their time limits. I coded the first problem quite easily but on the second and the third problem , my code could only pass a few test cases and gave TLE for most of them. Both the questions required very efficient solution and the last 5 to 10 Test Cases carried more weight than the rest so I didn't get through this round.

Q1. 
Print the Kth Digit
Given three non-negative integers N, M, and K, compute the Kth digit from the right in the number obtained from N raised to the power M (i.e., N ^ M).
Input:
The first line contains ...read more
Ans. 
The task is to find the Kth digit from the right in the number obtained from N raised to the power M.
• Iterate through the digits of N^M from right to left

• Keep track of the position of the current digit

• Return the digit at position K from the right
Answered by AI
Add your answer
Q2. 
The Skyline Problem
Compute the skyline of given rectangular buildings in a 2D city, eliminating hidden lines and forming the outer contour of the silhouette when viewed from a distance. Each building is ...read more
Ans. 
Compute the skyline of given rectangular buildings in a 2D city, eliminating hidden lines and forming the outer contour of the silhouette.
• Iterate through the buildings and create a list of critical points (x, y) where the height changes.

• Sort the critical points based on x-coordinate and process them to form the skyline.

• Merge consecutive horizontal segments of equal height into one to ensure no duplicates.

• Return the fin...read more
Answered by AI
Add your answer
Q3. 
Longest Palindromic Substring Problem Statement
You are provided with a string STR of length N. The goal is to identify the longest palindromic substring within this string. In cases where multiple palind...read more
Ans. 
Identify the longest palindromic substring in a given string.
• Iterate through the string and expand around each character to find palindromes

• Keep track of the longest palindrome found

• Return the longest palindrome with the smallest start index
Answered by AI
Add your answer

Round duration - 120 minutes
Round difficulty - Medium

The Entire Test is held in HackerRank Platform. It has: 
2 coding questions (one easy and one medium)
2 output questions(medium)
2 Aptitude(easy)
1 general Computer science(medium)
It took me 30 min for each coding questions. I did not know that general question is related to bash commands.
Tips: Practice the Warmup questions in Hacker Rank.
Do some Basic aptitude questions.
Thorough with the basic C and C++ concepts

Q1. 
Binary Tree to Doubly Linked List
Transform a given Binary Tree into a Doubly Linked List.
Ensure that the nodes in the Doubly Linked List follow the Inorder Traversal of the Binary Tree.
Input:
The fi...read more
Ans. 
Convert a Binary Tree into a Doubly Linked List following Inorder Traversal.
• Perform Inorder Traversal of the Binary Tree to get the nodes in order.

• Create a Doubly Linked List by linking the nodes in the order obtained from Inorder Traversal.

• Return the head of the Doubly Linked List as the output.
Answered by AI
Add your answer
Q2. 
Unique Element in Array
Given an arbitrary array arr consisting of N non-negative integers where every element appears thrice except for one. Your task is to find the element in the array that appears onl...read more
Ans. 
Find the unique element in an array where every other element appears thrice.
• Use XOR operation to find the unique element.

• Iterate through the array and XOR each element to find the unique one.

• Return the unique element as the answer.
Answered by AI
Add your answer

Round duration - 60 minutes
Round difficulty - Medium

It's completely around the data structures. The questions are a bit tricky but once u think without any tension u can get through easily. The interviewer is helpful and gives u few hints if u catch them at the right point of time u got it. 
Tips: got through Data Structures and Algorithms Made Easy by Narasimha Karumanchi. It's a best book for the interviews.

Q1. 
Binary Tree Traversals Problem Statement
Given a Binary Tree with 'N' nodes, where each node holds an integer value, your task is to compute the In-Order, Pre-Order, and Post-Order traversals of the binar...read more
Ans. 
Implement a function to compute In-Order, Pre-Order, and Post-Order traversals of a Binary Tree given in level-order format.
• Parse the input level-order tree elements to construct the binary tree.

• Implement recursive functions for In-Order, Pre-Order, and Post-Order traversals.

• Return the traversals as lists of lists for each test case.
Answered by AI
Add your answer
Q2. 
Delete N Nodes After M Nodes in a Linked List
Given a singly linked list and two integers 'N' and 'M', traverse the linked list to retain 'M' nodes and then delete the next 'N' nodes. Continue this proces...read more
Ans. 
Traverse a linked list to retain 'M' nodes and then delete the next 'N' nodes, repeating until the end of the list.
• Create a function that takes the head of the linked list, 'N', and 'M' as input parameters.

• Traverse the linked list, retaining 'M' nodes and deleting the next 'N' nodes in each iteration.

• Update the pointers accordingly to skip 'N' nodes after retaining 'M' nodes.

• Repeat this process until the end of the lin...read more
Answered by AI
Add your answer

Round duration - 60 minutes
Round difficulty - Easy

The interviewer asked to put everything on the blackboard and write down the code of each and everything.

Question : Explain all the search algorithm you know with space and Time complexities. 
Answer : Linear search : It is a sequential search algorithm where the entire array is traversed till the desired element is not found. Time complexity is O(N) and auxiliary space is O(1). 
Binary search : In this algorithm, a sorted array is searched by repeatedly dividing the search interval in half. 
Steps : 
1. Initially the interval covers the whole array.
2. If the value to be searched is less than the item in the middle of the interval, narrow the interval to the lower half. Otherwise, narrow it to the upper half. 
3. The process is repeated until the value is found or the interval is empty.
Time complexity is O(log n) and auxiliary space is O(1) in case of iterative implementation.

Q1. 
Maximum Frequency Number Problem Statement
Given an array of integers with numbers in random order, write a program to find and return the number which appears the most frequently in the array.
If multip...read more
Ans. 
Program to find the number with maximum frequency in an array of integers.
• Create a dictionary to store the frequency of each number in the array.

• Iterate through the array and update the frequency count in the dictionary.

• Find the number with the maximum frequency in the dictionary and return it.

• If multiple elements have the same maximum frequency, return the one with the lowest index.
Answered by AI
Add your answer

Round duration - 90 minutes
Round difficulty - Easy

Myntra had conducted a coding test on campus before the start of the placement season with 2 questions, one on stack and other on DP.
Tips : For the test, the DP question asked was pretty standard, on Longest Common Subsequence. The question on stacks, I don't remember what it was but it was also pretty straight forward. For the test, I would recommend to solve problem from GFG. If they do come to resume shortlisting, they are looking for people who have done good projects and internships.

Q1. 
Longest Common Subsequence Problem Statement
Given two strings STR1 and STR2, determine the length of their longest common subsequence.
A subsequence is a sequence that can be derived from another sequen...read more
Ans. 
The task is to find the length of the longest common subsequence between two given strings.
• Implement a function to find the longest common subsequence between two strings.

• Use dynamic programming to solve this problem efficiently.

• Iterate through the strings and build a matrix to store the lengths of common subsequences.

• Return the length of the longest common subsequence found.
Answered by AI
Add your answer

Round duration - 60 minutes
Round difficulty - Easy

The interview started off with questions on my general interest in Software Development. The first round had two coding questions, I was supposed to write the code on paper. 
For the questions, they asked me to code the solution first. And then gave a specific input and asked me to demonstrate step by step in my code, how it would lead to the correct answer.
Tips: It's ok if you can't code a general solution, if you can write a code which works for the particular input they have given then also it's ok with them. But be thorough with Data structures.

Q1. 
Add Two Numbers as Linked Lists
You are given two singly linked lists, where each list represents a positive number without any leading zeros.
Your task is to add these two numbers and return the sum as ...read more
Ans. 
Add two numbers represented as linked lists and return the sum as a linked list.
• Traverse both linked lists simultaneously while keeping track of carry from previous sum

• Create a new linked list to store the sum, updating the value and carry as needed

• Handle cases where one linked list is longer than the other by adding remaining digits with carry
Answered by AI
Add your answer

Round duration - 60 minutes
Round difficulty - Medium

I wasn't asked to write any code in this interview. They asked me some questions on Machine Learning, because of my projects in them. Then they asked me if I knew graph algorithms. Since I knew BFS and DFS, I told them. They asked the difference between the two. Then they asked me if I knew how to find the shortest distance between two points in a graph. I didn't know Dijkstra's properly but I knew it worked on the greedy approach so was able to tell that. Then they asked me how would I find the second shortest path. I tried to answer it with the same greedy approach, but couldn't arrive at the complete solution.
Tips: They ask a tough theoretical question. It's ok if you don't know the answer, they only look for your approach.

Q1. 
BFS Traversal in a Graph
Given an undirected and disconnected graph G(V, E) where V vertices are numbered from 0 to V-1, and E represents edges, your task is to output the BFS traversal starting from the ...read more
Ans. 
BFS traversal in a disconnected graph starting from vertex 0.
• Use a queue to keep track of nodes to visit next in BFS traversal

• Start traversal from vertex 0 and explore its neighbors first

• Continue exploring neighbors level by level until all nodes are visited

• Ensure to print connected nodes in numerical sort order
Answered by AI
Add your answer
Q2. 
DFS Traversal Problem Statement
Given an undirected and disconnected graph G(V, E), where V is the number of vertices and E is the number of edges, the connections between vertices are provided in the 'GR...read more
Ans. 
DFS traversal to find connected components in an undirected and disconnected graph.
• Perform DFS traversal on each vertex to find connected components

• Maintain a visited array to keep track of visited vertices

• Print the vertices of each connected component in ascending order
Answered by AI
Add your answer
Q3. 
Dijkstra's Shortest Path Problem
Given an undirected graph with ‘V’ vertices (labeled 0, 1, ... , V-1) and ‘E’ edges, where each edge has a weight representing the distance between two connected nodes (X,...read more
Ans. 
Dijkstra's algorithm is used to find the shortest path from a source node to all other nodes in a graph with weighted edges.
• Implement Dijkstra's algorithm to find the shortest path distances from the source node to all other nodes in the graph.

• Use a priority queue to efficiently select the next node with the shortest distance.

• Update the distances of neighboring nodes based on the current node's distance and edge weight...read more
Answered by AI
Add your answer