Amazon BDM Interview Questions and Answers

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
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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
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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
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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.
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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.
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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.
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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
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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.
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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.
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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
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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
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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
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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
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Round duration - 120 minutes
Round difficulty - Medium

This was a 2 hour round consisting of 5 mcqs and 2 codes. The mcqs were pretty much simple based on DS, DBMS, OS, OOP, and C.

Q1. 
Rabbit Jumping Problem
Consider 'n' carrots numbered from 1 to 'n' and 'k' rabbits. Each rabbit jumps to carrots only at multiples of its respective jumping factor A_j (i.e., A_j, 2A_j, 3A_j, ...), for all ra...read more
Ans. 
Calculate uneaten carrots by rabbits with specific jumping factors.
• Iterate through each carrot and check if any rabbit jumps on it.

• Use the jumping factors to determine which carrots are eaten.

• Subtract the eaten carrots from the total to get the uneaten count.
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Q2. 
Flip Bits Problem Explanation
Given an array of integers ARR of size N, consisting of 0s and 1s, you need to select a sub-array and flip its bits. Your task is to return the maximum count of 1s that can b...read more
Ans. 
Given an array of 0s and 1s, find the maximum count of 1s by flipping a sub-array at most once.
• Iterate through the array and keep track of the maximum count of 1s obtained by flipping a sub-array.

• Consider flipping a sub-array from index i to j by changing 0s to 1s and vice versa.

• Update the maximum count of 1s if the current count after flipping is greater.

• Return the maximum count of 1s obtained by flipping a sub-array
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Round duration - 60 minutes
Round difficulty - Medium

Started with a brief discussion on my projects and internships. A thorough discussion on whichever languages, frameworks I had used in my projects. Followed by discussion on coding questions. Apart from the codes there were some questions on OS, process stack, heap memory in Java, Garbage collection, OOP principles and comparison based sorting

Q1. 
Sum of Maximum and Minimum Elements Problem Statement
Given an array ARR of size N, your objective is to determine the sum of the largest and smallest elements within the array.
Follow Up:
Can you achie...read more
Ans. 
Find sum of maximum and minimum elements in an array with least number of comparisons.
• Iterate through the array and compare each element with current maximum and minimum to update them.

• Initialize max as smallest possible value and min as largest possible value.

• Return the sum of max and min after iterating through the array.
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Q2. 
Invert a Binary Tree Problem Statement
Given a Binary Tree and one of its leaf nodes, invert the binary tree by following these guidelines:
• The given leaf node becomes the root after the inversion. • F...read more
Ans. 
Invert a binary tree based on a given leaf node as the root.
• Start by finding the leaf node in the binary tree.

• Move the left child of the leaf node to the right side of the leaf node.

• Make the parent of the leaf node the left child of the leaf node.

• Repeat the process for each test case.

• Return the inverted binary tree in level order format.
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Round duration - 60 minutes
Round difficulty - Medium

Questions based on programming, DBMS and puzzles were asked in this round.

Q1. 
Rearrange Array to Form Largest Number
Given an array ARR consisting of non-negative integers, rearrange the numbers to form the largest possible number. The digits within each number cannot be changed.
...read more
Ans. 
Rearrange the array elements to form the largest possible number by concatenating them.
• Sort the array elements in a custom way where the concatenation of two numbers results in a larger number.

• Use a custom comparator function while sorting the array elements.

• Convert the sorted array elements to a single string to get the largest possible number.
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Q2. What is indexing in the context of databases?
Ans. 
Indexing in databases is a technique used to improve the speed of data retrieval by creating a data structure that allows for quick lookups.
• Indexes are created on columns in a database table to speed up the retrieval of rows that match a certain condition.

• They work similar to the index in a book, allowing the database to quickly find the relevant data without having to scan the entire table.

• Examples of indexes include ...read more
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Q3. What are the advantages of B+ Trees in database management systems?
Ans. 
B+ Trees are advantageous in database management systems due to their ability to efficiently store and retrieve data.
• B+ Trees have a high fanout, allowing for more keys to be stored in each node, reducing the height of the tree and improving search performance.

• B+ Trees are balanced trees, ensuring that operations like search, insertion, and deletion have a predictable time complexity of O(log n).

• B+ Trees are optimized ...read more
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Round duration - 45 minutes
Round difficulty - Medium

Puzzles and HR based questions were asked in this round.
He asked questions like : what are my career goals, what do you look forward to in a boss , how do you see yourself in 5 years ,etc etc .