MasterCard Senior Software Engineer 1 Interview Questions and Answers

Round duration - 60 minutes
Round difficulty - Medium

It was held in the evening around 4 pm. The camera was on during the test to invigilate the activity of students. On any doubtful action, warning was given. Platform was easy to code in.

Q1. 
Replace 0s Problem Statement
You are given a matrix where every element is either a 1 or a 0. The task is to replace 0 with 1 if it is surrounded by 1s. A 0 (or a set of 0s) is considered to be surrounded...read more
Ans. 
Given a matrix of 1s and 0s, replace 0s surrounded by 1s with 1s.
• Iterate through the matrix and check each 0 surrounded by 1s.

• If a 0 is surrounded by 1s, replace it with 1.

• Update the matrix in place without printing or returning it.
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Q2. 
Ways To Make Coin Change
Given an infinite supply of coins of varying denominations, determine the total number of ways to make change for a specified value using these coins. If it's not possible to make...read more
Ans. 
The task is to determine the total number of ways to make change for a specified value using given denominations.
• Use dynamic programming to keep track of the number of ways to make change for each value up to the target value.

• Iterate through each denomination and update the number of ways to make change for each value based on the current denomination.

• Handle base cases such as making change for 0 or using only the smal...read more
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Q3. 
Minimum Subset Sum Difference Problem
Given an array of non-negative integers, your task is to partition this array into two subsets such that the absolute difference between the sums of the subsets is mi...read more
Ans. 
Given an array, partition it into two subsets to minimize the absolute difference between their sums.
• Use dynamic programming to calculate all possible subset sums.

• Iterate through the subset sums to find the minimum absolute difference.

• Consider all possible partitions of the array elements.

• Example: For input [1, 6, 11, 5], the minimum absolute difference is 1.

• Example: For input [1, 2, 3], the minimum absolute difference
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Round duration - 60 minutes
Round difficulty - Medium

It was held in the morning around 11:30 am. The interview was scheduled on google meet. The interviewer was quite friendly. He started by a brief introduction. This round was mostly based on Data structures and algorithms. At the end he asked some concepts of OOPs and Operating System.

Q1. 
String Transformation Problem
Given a string (STR) of length N, you are tasked to create a new string through the following method:
Select the smallest character from the first K characters of STR, remov...read more
Ans. 
Given a string and an integer K, create a new string by selecting the smallest character from the first K characters of the input string and repeating the process until the input string is empty.
• Iterate through the input string, selecting the smallest character from the first K characters each time.

• Remove the selected character from the input string and append it to the new string.

• Continue this process until the input ...read more
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Q2. 
SpecialStack Design Problem
Design a stack that efficiently supports the getMin() operation in O(1) time with O(1) extra space. This stack should include the following operations: push(), pop(), top(), is...read more
Ans. 
Design a stack that supports getMin() operation in O(1) time with O(1) extra space using inbuilt stack data structure.
• Use two stacks - one to store the actual data and another to store the minimum value at each level.

• When pushing a new element, check if it is smaller than the current minimum and update the minimum stack accordingly.

• When popping an element, also pop the top element from the minimum stack if it matches t...read more
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Q3. 
Geometric Progression Subsequences Problem Statement
Given an array of ‘N’ integers, determine the number of subsequences of length 3 that form a geometric progression with a specified common ratio ‘R’.
...read more
Ans. 
Count the number of subsequences of length 3 forming a geometric progression with a specified common ratio in an array of integers.
• Iterate through the array and for each element, check for possible subsequences of length 3 with the given common ratio.

• Use a hashmap to store the count of possible subsequences for each element as the middle element.

• Return the total count of subsequences modulo 10^9 + 7.

• Example: For input ...read more
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Q4. What are the conditions for a deadlock to occur?
Ans. 
Deadlock occurs when two or more processes are waiting for each other to release resources, resulting in a standstill.
• Two or more processes must be holding resources and waiting for resources held by other processes

• Processes cannot proceed because they are stuck in a circular wait

• Resources cannot be forcibly released by the operating system

• Examples: Process A holds Resource 1 and waits for Resource 2, while Process B h
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Round duration - 45 minutes
Round difficulty - Medium

It was held in the afternoon around 3pm. The interviewer was quite friendly. She started with my introduction. She asked 2-3 problems related to data structures and then asked about python libraries which I used in my projects.

Q1. 
Group Anagrams Problem Statement
Given an array or list of strings called inputStr, your task is to return the strings grouped as anagrams. Each group should contain strings that are anagrams of one anoth...read more
Ans. 
Group anagrams in an array of strings based on their characters.
• Iterate through each string in the input array/list.

• For each string, sort the characters alphabetically to create a key for grouping.

• Use a hashmap to group strings with the same key.

• Return the grouped anagrams as separate arrays of strings.
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Q2. 
Kth Smallest Element Problem Statement
You are provided with an array of integers ARR of size N and an integer K. Your task is to find and return the K-th smallest value present in the array. All elements...read more
Ans. 
Find the K-th smallest element in a given array of distinct integers.
• Sort the array in ascending order.

• Return the element at index K-1 from the sorted array.

• Handle edge cases like K being out of bounds or array being empty.
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Round duration - 45 minutes
Round difficulty - Medium

It was held in the evening around 6 pm. The interviewer started with a brief introduction of me. He asked about my projects and then asked some concepts of Operating System and problems related to data structures. I had projects of Machine Learning and Deep learning. Discussion about projects continued for about 25 minutes.

Q1. 
Middle of a Linked List
You are given the head node of a singly linked list. Your task is to return a pointer pointing to the middle of the linked list.
If there is an odd number of elements, return the ...read more
Ans. 
Return the middle element of a singly linked list, or the one farther from the head node if there are even elements.
• Traverse the linked list with two pointers, one moving twice as fast as the other

• When the fast pointer reaches the end, the slow pointer will be at the middle

• Return the element pointed to by the slow pointer
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I dont remember exact questions but they are like leetcode easy and medium

Q1. How web/internet works?
Ans. 
The web/internet is a network of interconnected devices that communicate through standardized protocols to share information.
• Devices connect to the internet through ISPs

• Data is transmitted through packets using TCP/IP protocols

• Web browsers use HTTP/HTTPS protocols to request and receive web pages

• DNS servers translate domain names to IP addresses

• Web servers host web pages and respond to requests

• Search engines use web cr
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Q2. Coding questions with complete explanation
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Q1. Coding and managerial round similar to round 2
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Round duration - 70 minutes
Round difficulty - Easy

The first round was the Online Coding Round of 70 minutes with 3 problems of 3 marks, 3 marks, and 4 marks respectively.
The first two questions were easy and the third one was a bit tricky. The round started at 6 PM. 
Anyone who is practicing continuously could have solved these questions easily within the time limit. The test cases were also not so hard and distinct. I coded in C++ language.
The questions asked were-
1. Minimum insertions required to make a string palindrome
2. To find the distance of the closest leaf from a node with given data.
3. Add two numbers represented by linked lists

22 students were selected for the next round.

Q1. 
Minimum Insertions to Make a String Palindrome
Determine the minimal number of characters needed to insert into a given string STR to transform it into a palindrome.
Example:
Input:
STR = "abcaa"
Outp...read more
Ans. 
The task is to find the minimum number of characters needed to insert into a given string to make it a palindrome.
• Use dynamic programming to find the longest palindromic subsequence of the given string.

• Subtract the length of the longest palindromic subsequence from the length of the original string to get the minimum insertions required.

• Handle edge cases like an empty string or a string that is already a palindrome.

• Exa...read more
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Q2. 
Closest Leaf in a Binary Tree
Ninja is stuck in a maze represented as a binary tree, and he is at a specific node ‘X’. Help Ninja find the shortest path to the nearest leaf node, which is considered an ex...read more
Ans. 
Find the minimum distance from a given node to the nearest leaf node in a binary tree.
• Traverse the binary tree from the given node 'X' to find the nearest leaf node using BFS or DFS.

• Keep track of the distance from 'X' to each leaf node encountered during traversal.

• Return the minimum distance found as the output.
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Q3. 
Adding Two Linked Lists
Given two singly linked lists, with each list representing a positive number without leading zeros, your task is to add these two numbers and return the result in the form of a new...read more
Ans. 
Add two numbers represented by linked lists and return the result as a new linked list.
• Traverse both linked lists simultaneously while adding corresponding elements and carry over the sum if needed

• Handle cases where one linked list is longer than the other

• Create a new linked list to store the sum of the two numbers
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Round duration - 80 minutes
Round difficulty - Easy

It was a technical interview. The platform used was google meet for online video calling. The interviewer first introduced himself then asked me to introduce myself. He also asked about my well-being amid the Covid-19 pandemic. He asked me 3 problems from data structures. He put a lot of focus on my project. We discussed about my project for about 20 mins. He asked various questions related to my project and I answered them confidently. After 70-75 mins he said that interview was over and that I may ask him anything. I asked him to give me feedback about my resume and my project. He gave me advice to improve my resume and the interview was over. The first technical interview was easy and was not so challenging as I was prepared.

Q1. 
All Pairs with Target Sum
Given an array of integers ARR with length 'N' and an integer 'Target', the task is to find all unique pairs of elements that add up to the 'Target'.
Input:
First line: Integer...read more
Ans. 
Find all unique pairs of elements in an array that add up to a given target sum.
• Use a hashmap to store the difference between the target sum and each element as keys and their indices as values.

• Iterate through the array and check if the current element's complement exists in the hashmap.

• Return the pairs of elements that add up to the target sum.
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Q2. 
Quick Sort Problem Statement
Sort the given array of integers in ascending order using the quick sort algorithm. Quick sort is a divide-and-conquer algorithm where a pivot point is chosen to partition the...read more
Ans. 
Implement quick sort algorithm to sort an array of integers in ascending order.
• Choose a pivot element (e.g., rightmost element) to partition the array into two subarrays.

• Recursively apply quick sort on the subarrays until the entire array is sorted.

• Time complexity can be optimized to NlogN for worst-case scenarios.
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Q3. 
Merge Sort Task
Given a sequence of numbers, denoted as ARR, your task is to return a sorted sequence of ARR in non-descending order using the Merge Sort algorithm.
Example:
Explanation:
The Merge Sort...read more
Ans. 
Implement Merge Sort algorithm to sort a sequence of numbers in non-descending order.
• Implement the Merge Sort algorithm which involves dividing the array into two halves, sorting each half, and then merging them back together.

• Recursively call the Merge Sort function on each half of the array until the base case of having a single element in the array is reached.

• Merge the sorted halves back together in a new array in no...read more
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Round duration - 60 minutes
Round difficulty - Medium

This was also a technical round. The interviewer focused on data structures and resume. Apart from some basic questions about my resume, he asked majorly about data structures and algorithms. The interview was an hour long and he asked only 2 problems. Both of them were from trees. In this round, he focused if I can change my approach if a slight change is made in the question. Like he asked me to write code for inorder traversal. Obviously, I used a recursive approach. He then asked me to use the iterative method to find inorder traversal of the tree.

The questions he asked were-
1. Inorder traversal (both recursive and iterative method)
2. Level Order Traversal
( For obvious reasons I knew level order traversal very well. I coded it swiftly, so he asked me to write code for Zig-Zag traversal)

Q1. 
Inorder Successor in a Binary Tree
Find the inorder successor of a given node in a binary tree. The inorder successor is the node that appears immediately after the given node during an inorder traversal....read more
Ans. 
Find the inorder successor of a given node in a binary tree.
• Perform an inorder traversal of the binary tree to find the successor of the given node.

• If the given node has a right child, the successor will be the leftmost node in the right subtree.

• If the given node does not have a right child, backtrack to the parent nodes to find the successor.
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Q2. 
Zigzag Traversal of Binary Tree
Given a binary tree with integer values in its nodes, your task is to print the zigzag traversal of the tree.
Note:
In zigzag order, level 1 is printed from left to right...read more
Ans. 
Implement a function to print the zigzag traversal of a binary tree.
• Use a queue to perform level order traversal of the binary tree.

• Maintain a flag to switch between printing nodes from left to right and right to left at each level.

• Store nodes at each level in a list and reverse the list if the flag is set to print in zigzag order.
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Round duration - 50 minutes
Round difficulty - Medium

This was the final round of the Interview process. My interview was scheduled for 7.30 PM. It started at approximately 7.40 PM. The main focus of the interviewer was on my projects and my skills. He asked me many questions regarding my project like what problems I faced, what did you learn from this, apart from developing skills what else did you learn while developing the project, why did you use this tech instead of this, security features, scalability of the project and many more. I answered almost every question as perfectly as I can. Later he asked me some basic questions from NodeJS (as I am a full stack developer). In the end, he asked a puzzle. I didn't know the solution to the puzzle but we discussed it and I figured out the solution.