Box8 Software Developer Intern Interview Questions and Answers

Round duration - 60 minutes
Round difficulty - Medium

Q1. 
Longest Increasing Subsequence Problem Statement
Given an array of integers with 'N' elements, determine the length of the longest subsequence where each element is greater than the previous element. This...read more
Ans. 
Find the length of the longest strictly increasing subsequence in an array of integers.
• Use dynamic programming to keep track of the longest increasing subsequence ending at each element.

• Initialize an array to store the length of the longest increasing subsequence ending at each index.

• Iterate through the array and update the length of the longest increasing subsequence for each element.

• Return the maximum value in the ar...read more
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Q2. 
Digits Decoding Problem
Ninja has a string of characters from 'A' to 'Z', encoded using their numeric values (A=1, B=2, ..., Z=26). The encoded string is given as a sequence of digits (SEQ). The task is t...read more
Ans. 
The task is to determine the number of possible ways to decode a sequence of digits back into a string of characters from 'A' to 'Z'.
• Use dynamic programming to keep track of the number of ways to decode the sequence at each position.

• Consider different cases when decoding the sequence, such as single digit decoding and double digit decoding.

• Handle edge cases like '0' and '00' appropriately.

• Return the final count modulo
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Round duration - 60 minutes
Round difficulty - Medium

Q1. 
Leaves at Same Level Problem Statement
Given a binary tree with 'N' nodes, determine if all the leaf nodes are situated at the same level. Return true if all the leaf nodes are at the same level, otherwis...read more
Ans. 
Check if all leaf nodes in a binary tree are at the same level.
• Traverse the binary tree and keep track of the level of each leaf node.

• Compare the levels of all leaf nodes at the end to determine if they are at the same level.

• Use a queue for level order traversal of the binary tree.
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Q2. 
Maximum Non-Adjacent Subsequence Sum
Given an array of integers, determine the maximum sum of a subsequence without choosing adjacent elements in the original array.
Input:
The first line consists of an...read more
Ans. 
Find the maximum sum of a subsequence without choosing adjacent elements in an array.
• Use dynamic programming to keep track of the maximum sum of non-adjacent elements at each index.

• At each index, the maximum sum is either the sum of the current element and the element two positions back, or the sum at the previous index.

• Iterate through the array and update the maximum sum at each index accordingly.

• Return the maximum su
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Round duration - 60 minutes
Round difficulty - Medium

Q1. 
LRU Cache Design Question
Design a data structure for a Least Recently Used (LRU) cache that supports the following operations:
1. get(key) - Return the value of the key if it exists in the cache; otherw...read more
Ans. 
Design a Least Recently Used (LRU) cache data structure that supports get and put operations with capacity constraint.
• Use a combination of hashmap and doubly linked list to implement the LRU cache.

• Keep track of the least recently used item and update it accordingly when inserting new items.

• Ensure to handle the capacity constraint by evicting the least recently used item when the cache is full.

• Implement get(key) and put...read more
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Q2. What is the difference between Mutex and Semaphores?
Ans. 
Mutex is used for exclusive access to a resource by only one thread at a time, while Semaphores can allow multiple threads to access a resource simultaneously.
• Mutex is binary and can be locked by only one thread at a time, while Semaphores can have a count greater than one.

• Mutex is used for protecting critical sections of code, while Semaphores can be used for controlling access to a pool of resources.

• Mutex is simpler ...read more
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Q3. Given the employee and department tables, how would you find the number of employees in each department? (This question focuses on SQL Joins.)
Ans. 
Use SQL Joins to find the number of employees in each department.
• Use a JOIN statement to combine the employee and department tables based on the department ID.

• Group the results by department ID and use COUNT() function to find the number of employees in each department.

• Example: SELECT department.department_id, COUNT(employee.employee_id) AS num_employees FROM department JOIN employee ON department.department_id = emplo...read more
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Round duration - 90 minutes
Round difficulty - Medium

Coding question of medium level difficulty, from DP. 
18 MCQs were core CSE related concepts e.g: OS, OOPs, DBMS, Networking
Time was 90 minutes.

Q1. 
Minimum Cost to Destination
You are given an NxM matrix consisting of '0's and '1's. A '1' signifies that the cell is accessible, whereas a '0' indicates that the cell is blocked. Your task is to compute ...read more
Ans. 
Find the minimum cost to reach a destination in a matrix with blocked cells.
• Use Breadth First Search (BFS) algorithm to explore all possible paths from the starting point to the destination.

• Keep track of the cost incurred at each cell and update it as you move through the matrix.

• Return the minimum cost to reach the destination or -1 if it is unreachable.
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Round duration - 30 minutes
Round difficulty - Medium

It was an one-to-one interview. It checks your problem solving ability and a few OOPs, OS, DBMS etc concepts. Coding questions were related to array, queue and DP.

Q1. 
Triangle Formation Using Array Elements
Given an integer array/list ARR of length 'N', determine if it is possible to form at least one non-degenerate triangle using the values of the array as the sides o...read more
Ans. 
Determine if it is possible to form a non-degenerate triangle using array elements as sides.
• Check if the sum of any two sides is greater than the third side for all combinations of sides.

• If the above condition is met for any combination, return true; otherwise, return false.
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Q2. 
Maximum Sum of Non-Adjacent Elements
You are given an array/list of integers. The task is to return the maximum sum of a subsequence such that no two elements in the subsequence are adjacent in the given ...read more
Ans. 
Find the maximum sum of non-adjacent elements in an array.
• Use dynamic programming to keep track of the maximum sum at each index, considering whether to include the current element or not.

• At each index, the maximum sum can be either the sum excluding the current element or the sum including the current element but excluding the previous element.

• Iterate through the array and update the maximum sum accordingly.

• Example: F...read more
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Round duration - 45 minutes
Round difficulty - Easy

It was also a problem solving round. However after coding questions, they also asked CSE conceptual questions.

Q1. 
Sum Tree Conversion
Convert a given binary tree into its sum tree. In a sum tree, every node's value is replaced with the sum of its immediate children's values. Leaf nodes are set to 0. Finally, return th...read more
Ans. 
Convert a binary tree into a sum tree by replacing each node's value with the sum of its children's values. Return preorder traversal.
• Traverse the tree in a bottom-up manner, starting from the leaf nodes.

• For each node, update its value to the sum of its children's values.

• Set leaf nodes to 0.

• Return the preorder traversal of the modified tree.
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Q2. What are the core concepts of indexing in Database Management Systems (DBMS)?
Ans. 
Core concepts of indexing in DBMS include types of indexes, benefits of indexing, and factors affecting index performance.
• Types of indexes: B-tree, Hash, Bitmap, etc.

• Benefits of indexing: Faster data retrieval, improved query performance, reduced disk I/O.

• Factors affecting index performance: Selectivity, clustering factor, index fragmentation.

• Examples: Creating an index on a column in a table to speed up search queries
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Q1. Basic Php ,Oops
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Q1. Security questions
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Round duration - 90 minutes
Round difficulty - Medium

The test was scheduled at 2:30 PM, IST. The test was conducted online, due to the ongoing pandemic situation. Webcam was required to be switched on during the complete duration of the test. I had solved 2/2 coding questions with all test cases successfully passing. Out of the 10 MCQ questions, I had done 6. Around 90 students sat for the online coding round, 19 were shortlisted for the interview. Those who had solved both coding questions were called for interview.

Q1. 
Candies Distribution Problem Statement
Prateek is a kindergarten teacher with a mission to distribute candies to students based on their performance. Each student must get at least one candy, and if two s...read more
Ans. 
The task is to distribute candies to students based on their performance while minimizing the total candies distributed.
• Iterate through the array of student ratings to determine the minimum number of candies required.

• Assign each student at least one candy.

• Adjust the number of candies based on the ratings of adjacent students to minimize the total candies distributed.

• Example: For ratings [5, 8, 1, 5, 9, 4], the optimal ...read more
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Q2. 
Problem Statement: Minimum Cost to Buy Ninja Blades
Ninja Yuki wants to purchase ninja blades at the Spring Fair in his village. Initially, he has 0 blades, and his goal is to buy 'N' blades. The merchant...read more
Ans. 
Calculate the minimum cost to acquire a specific number of ninja blades using a given pricing mechanism.
• Iterate through each test case to determine the minimum cost needed to acquire the desired number of blades.

• Consider the cost of adding 1 blade versus doubling the current number of blades to reach the target quantity.

• Keep track of the total cost as blades are acquired based on the pricing mechanism.

• Return the minimu
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Round duration - 60 minutes
Round difficulty - Medium

This was a pure DSA based round. Two questions were asked in this round. The interviewer was quite good, and helped in between.

Q1. 
First Unique Character in a Stream Problem Statement
Given a string A consisting of lowercase English letters, determine the first non-repeating character at each point in the stream of characters.
Examp...read more
Ans. 
Given a string of lowercase English letters, find the first non-repeating character at each point in the stream.
• Iterate through the characters in the string and maintain a count of each character.

• Use a queue to keep track of the order of characters encountered.

• For each character, check if it is the first non-repeating character by looking at its count in the map.

• If a character's count is 1, it is the first non-repeatin...read more
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Q2. 
Boolean Matrix Transformation Challenge
Given a 2-dimensional boolean matrix mat of size N x M, your task is to modify the matrix such that if any element is 1, set its entire row and column to 1. Specifi...read more
Ans. 
Modify a boolean matrix such that if any element is 1, set its entire row and column to 1 in-place.
• Iterate through the matrix to find elements with value 1.

• Use additional arrays to keep track of rows and columns to be modified.

• Update the matrix in-place based on the identified rows and columns.
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Round duration - 75 minutes
Round difficulty - Medium

This round was also again focused on DSA. Two interviewers were present. This round was very extensive and everything was asked in depth as well as they asked to write the codes as well for all the questions. I was also asked to explain my projects, they were based on ML. Many aspects of OOPs, POP, memory allocation was asked as well.

Q1. 
Maximum Sum of Index-Multiplied Rotations
Given an array ARR of size N, determine the maximum sum of i * ARR[i] possible through any number of rotations. Both left and right rotations are allowed, and can...read more
Ans. 
Find maximum sum of i * ARR[i] possible through any number of rotations in an array.
• Calculate the sum of i * ARR[i] for each rotation and find the maximum sum.

• Consider both left and right rotations.

• Optimize the solution to avoid redundant calculations.

• Handle edge cases like empty array or single element array.
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Q2. 
Averages of Levels in Binary Tree Problem Statement
Given an arbitrary binary tree consisting of 'N' nodes numbered from 1 to 'N'. Each node is associated with a positive integer value. Your task is to ca...read more
Ans. 
Calculate the average of node values at each level in a binary tree.
• Traverse the binary tree level by level using BFS

• Calculate the sum of node values at each level and divide by the number of nodes at that level

• Print the floor value of the average for each level
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Round duration - 90 minutes
Round difficulty - Medium

Q1. 
Rotate Matrix Right K Times
You are given a matrix MAT of size 'N' * 'M', where 'N' is the number of rows and 'M' is the number of columns, along with a positive integer 'K'. Your task is to rotate the ma...read more
Ans. 
Rotate a matrix to the right 'K' times by shifting each column to the right 'K' times.
• Iterate 'K' times to perform right rotation on the matrix

• Shift each column to the right by one position in each rotation

• Handle wrapping around the matrix when shifting columns

• Return the matrix elements row-wise after 'K' rotations
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Q2. 
Word Search Problem Statement
Given a two-dimensional grid of size N x M consisting of upper case characters and a string 'WORD', determine how many times the 'WORD' appears in the grid.
The 'WORD' can b...read more
Ans. 
Count how many times a given word appears in a 2D grid by moving in any of the eight possible directions.
• Iterate through each cell in the grid and check if the word can be formed starting from that cell in any of the eight directions.

• Use recursion to explore all possible paths from a starting cell to form the word.

• Keep track of visited cells to avoid revisiting the same cell in the same path.

• Return the count of how man
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Round duration - 75 minutes
Round difficulty - Medium

Interview started with an introduction and walk through the resume for first 5 minutes. After that, interview asked few coding questions.

Q1. 
Problem Statement: Largest Island
You are provided with a non-empty grid consisting of only 0s and 1s. Your task is to determine the maximum area of an island within the given grid.
An island consists of a...read more
Ans. 
Find the maximum area of an island in a grid of 0s and 1s.
• Iterate through the grid and perform depth-first search (DFS) to find connected 1s.

• Keep track of the area of each island found and return the maximum area.

• Consider all four directions (horizontal, vertical, and diagonal) while exploring the island.

• Handle edge cases like grid boundaries and already visited cells during DFS.

• If no island is present, return 0 as the
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Q2. 
Pythagorean Triplet Problem
Determine if there exists a Pythagorean triplet within a given array of integers. A Pythagorean triplet consists of three numbers, x, y, and z, such that x^2 + y^2 = z^2.
Expl...read more
Ans. 
Check if there exists a Pythagorean triplet in a given array of integers.
• Iterate through all possible triplets in the array and check if they form a Pythagorean triplet.

• Use a nested loop to generate all possible combinations of three numbers from the array.

• Check if the sum of squares of two numbers is equal to the square of the third number.
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Q3. 
Top View of Binary Tree Problem Statement
Given a Binary Tree of integers, you are tasked with finding the top view of the binary tree. The top view is the set of nodes visible when the tree is viewed fro...read more
Ans. 
Find the top view of a Binary Tree by returning a list of visible nodes when viewed from the top.
• Traverse the Binary Tree in level order and keep track of the horizontal distance of each node from the root.

• Use a map to store the nodes at each horizontal distance, and only keep the topmost node for each horizontal distance.

• Return the values of the topmost nodes in the map as the top view of the Binary Tree.
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Round duration - 90 minutes
Round difficulty - Medium

This round was focused on DSA along with short discussion on computer science fundamentals. For coding problems, I was asked to code the first problem only. For others, had to discuss the approach only. For computer science fundamentals, discussion on OOPS. Differences between process and threads were discussed.

Q1. 
Fixing a Swapped Binary Search Tree
Given a Binary Search Tree (BST) where two nodes have been swapped by mistake, your task is to restore or fix the BST without changing its structure.
Input:
The first...read more
Ans. 
Restore a Binary Search Tree by fixing two swapped nodes without changing its structure.
• Identify the two nodes that are swapped by mistake in the BST.

• Swap the values of the two identified nodes to restore the BST.

• Perform an in-order traversal of the BST to verify the correct restoration.

• Ensure no extra space other than the recursion stack is used for the solution.
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Q2. 
Implement Stack with Linked List
Your task is to implement a Stack data structure using a Singly Linked List.
Explanation:
Create a class named Stack which supports the following operations, each in O(1...read more
Ans. 
Implement a Stack data structure using a Singly Linked List with operations like getSize, isEmpty, push, pop, and getTop in O(1) time.
• Create a class named Stack with methods for getSize, isEmpty, push, pop, and getTop.

• Use a Singly Linked List to store the elements of the stack.

• Ensure that each operation runs in constant time O(1).

• Handle edge cases like empty stack appropriately.

• Test the implementation with sample queri
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Round duration - 90 minutes
Round difficulty - Hard

Timing was 11 am. Platform was quite well.

Q1. 
Rat in a Maze Problem Statement
You need to determine all possible paths for a rat starting at position (0, 0) in a square maze to reach its destination at (N-1, N-1). The maze is represented as an N*N ma...read more
Ans. 
Find all possible paths for a rat in a maze from source to destination.
• Use backtracking to explore all possible paths in the maze.

• Keep track of visited cells to avoid revisiting them.

• Recursively try moving in all directions (up, down, left, right) until reaching the destination.

• Add the path to the result list when the destination is reached.

• Sort the result list alphabetically before returning.
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Q2. 
Minimum Cost to Destination
You are given an NxM matrix consisting of '0's and '1's. A '1' signifies that the cell is accessible, whereas a '0' indicates that the cell is blocked. Your task is to compute ...read more
Ans. 
Find the minimum cost to reach a destination in a matrix with specified rules.
• Use BFS traversal to explore all possible paths from the starting point to the destination.

• Keep track of the cost incurred at each cell and update it accordingly.

• Return the minimum cost to reach the destination or -1 if unreachable.
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Q1. Sort an array in O(nlogn)
Ans. 
Use merge sort algorithm to sort the array in O(nlogn) time complexity.
• Implement merge sort algorithm which divides the array into two halves, recursively sorts the halves, and then merges the sorted halves.

• Time complexity of merge sort is O(nlogn) where n is the number of elements in the array.

• Example: ['apple', 'banana', 'cherry', 'date'] can be sorted using merge sort in O(nlogn) time complexity.
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Q2. Find element in sorted Array
Ans. 
Use binary search to find element in sorted array efficiently.
• Start with middle element and compare with target

• If target is less, search left half, if greater search right half

• Repeat until element is found or search space is empty
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