QSC, LLC Interview Questions and Answers

Round duration - 180 Minutes
Round difficulty - Medium

Round was held in the morning at 10 am.

Q1. 
M - Coloring Problem Statement
Given an undirected graph with 'N' nodes in the form of an adjacency matrix and an integer 'M', determine if it is possible to color the vertices of the graph using at most ...read more
Ans. 
The problem involves determining if a given graph can be colored with at most 'M' colors without adjacent vertices sharing the same color.
• Create a function that takes the adjacency matrix, number of nodes 'N', and maximum number of colors 'M' as input.

• Implement a graph coloring algorithm such as backtracking or greedy coloring to check if the graph can be colored with at most 'M' colors.

• Check if adjacent vertices have ...read more
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Round duration - 40 Minutes
Round difficulty - Medium

The round was held in the evening

Q1. 
Trie Data Structure Implementation
Design and implement a Trie (prefix tree) to perform the following operations:
• insert(word): Add a string "word" to the Trie.
• search(word): Verify if the string "w...read more
Ans. 
Implement a Trie data structure to insert, search, and check for prefixes in strings.
• Create a TrieNode class with children and isEndOfWord attributes.

• Implement insert, search, and startsWith methods in the Trie class.

• Use a Trie to efficiently store and search for strings based on prefixes.

• Example: insert 'apple', search 'apple' returns true, startsWith 'app' returns true, search 'app' returns false.
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Round duration - 10 Minutes
Round difficulty - Easy

Was held in the morning around 9 am

Round duration - 120 Minutes
Round difficulty - Medium

The round had 2 coding problems to solve with varying difficulty. Each candidate had a different set of questions. The round was around 2 pm. The webcam was turned on to keep an eye on candidates.

Q1. 
Bursting Balloons Problem
Given an array ARR of size N, where each element represents the height of a balloon. The task is to destroy all balloons by shooting arrows from left to right. When an arrow hits...read more
Ans. 
Find the minimum number of arrows needed to burst all balloons by shooting arrows from left to right.
• Sort the array in non-decreasing order to make it easier to calculate the minimum number of arrows needed.

• Iterate through the sorted array and count the number of times the height decreases compared to the previous balloon.

• The count of decreases + 1 will give the minimum number of arrows needed to burst all balloons.

• Exa...read more
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Q2. 
Count Leaf Nodes in a Binary Tree
Count the number of leaf nodes present in a given binary tree. A binary tree is a data structure where each node has at most two children, known as the left child and the...read more
Ans. 
Count the number of leaf nodes in a binary tree.
• Traverse the binary tree and check if both left and right children are NULL to identify leaf nodes.

• Use recursion to traverse the tree efficiently.

• Keep track of the count of leaf nodes as you traverse the tree.

• Handle base cases where the current node is NULL or a leaf node.
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Round duration - 60 Minutes
Round difficulty - Medium

This round had 2 questions related to DSA. I was first asked to explain my approach with proper complexity analysis and then code the soution in any IDE that I prefer.

Q1. 
Rod Cutting Problem Statement
Given a rod of a certain length, the rod can be divided into different sizes, each with an associated cost. Your task is to determine the maximum cost that can be obtained by...read more
Ans. 
The Rod Cutting Problem involves maximizing the profit obtained by cutting a rod into smaller pieces and selling them.
• Use dynamic programming to solve this problem efficiently.

• Create a table to store the maximum profit for each sub-length of the rod.

• Iterate through the rod lengths and update the table with the maximum profit.

• The final answer will be the maximum profit for the total length of the rod.
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Q2. 
Count Subarrays with Given XOR Problem Statement
You are given an array of integers ARR and an integer X. Your task is to determine the number of subarrays of ARR whose bitwise XOR is equal to X.
Example...read more
Ans. 
Count the number of subarrays in an array whose XOR is equal to a given value.
• Iterate through the array and keep track of XOR values and their frequencies using a hashmap.

• For each element in the array, calculate the XOR with the current element and check if the required XOR value exists in the hashmap.

• Increment the count of subarrays whenever the required XOR value is found in the hashmap.
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Round duration - 60 Minutes
Round difficulty - Medium

This round had 2 questions of DSA of Easy-Medium difficulty and at the end I was asked a Puzzle to check my general problem solving ability.

Q1. 
Rotting Oranges Problem Statement
You are given a grid containing oranges where each cell of the grid can contain one of the three integer values:
• 0 - representing an empty cell
• 1 - representing a fre...read more
Ans. 
Find the minimum time required to rot all fresh oranges in a grid.
• Use Breadth First Search (BFS) to simulate the rotting process of oranges.

• Keep track of the time taken to rot all oranges and the count of fresh oranges remaining.

• If all fresh oranges are not rotten after simulation, return -1.

• Handle edge cases like empty grid or no fresh oranges present.

• Example: For the given grid, the minimum time required is 4 seconds...read more
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Q2. 
Detect and Remove Loop in Linked List
For a given singly linked list, identify if a loop exists and remove it, adjusting the linked list in place. Return the modified linked list.
Expected Complexity:
A...read more
Ans. 
Detect and remove loop in a singly linked list in place with O(n) time complexity and O(1) space complexity.
• Use Floyd's Cycle Detection Algorithm to identify the loop in the linked list.

• Once the loop is detected, use two pointers approach to find the start of the loop.

• Adjust the pointers to remove the loop and return the modified linked list.

• Example: For input 5 2 and 1 2 3 4 5, return 1 2 3 4 5 without the loop.
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Q3. You have two wires of different lengths that are both capable of burning for exactly one hour when ignited at both ends. How can you measure a time interval of 45 minutes using these two wires?
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Round duration - 50 Minutes
Round difficulty - Medium

This round had 2 Algorithmic questions wherein I was supposed to code both the problems after discussing their
approaches and respective time and space complexities . After that , I was grilled on some OOPS concepts related to C++.

Q1. 
Longest Palindromic Substring Problem Statement
You are provided with a string STR of length N. The task is to find the longest palindromic substring within STR. If there are several palindromic substring...read more
Ans. 
Given a string, find the longest palindromic substring within it.
• Iterate through the string and expand around each character to find palindromes

• Keep track of the longest palindrome found so far

• Return the longest palindromic substring
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Q2. 
Quick Sort Problem Statement
You are provided with an array of integers. The task is to sort the array in ascending order using the quick sort algorithm.
Quick sort is a divide-and-conquer algorithm. It ...read more
Ans. 
Yes, the quick sort algorithm can be enhanced to achieve NlogN complexity in the worst case by using a randomized version of the algorithm.
• Randomized quick sort involves randomly selecting the pivot element to reduce the chances of worst-case scenarios.

• By choosing a random pivot, the algorithm becomes less predictable and more likely to achieve the desired time complexity.

• This enhancement helps in avoiding the worst-ca...read more
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Q3. What are friend functions in C++?
Ans. 
Friend functions in C++ are functions that are not members of a class but have access to its private and protected members.
• Friend functions are declared inside a class with the keyword 'friend'.

• They can access private and protected members of the class.

• They are not member functions of the class, but have the same access rights as member functions.

• Friend functions are useful for implementing operators that are not part ...read more
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Q4. What is the difference between Early Binding and Late Binding in C++?
Ans. 
Early binding is resolved at compile time while late binding is resolved at runtime in C++.
• Early binding is also known as static binding, where the function call is resolved at compile time based on the type of the object.

• Late binding is also known as dynamic binding, where the function call is resolved at runtime based on the actual type of the object.

• Early binding is faster as the function call is directly linked to ...read more
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