Eternal Limited Software Developer Intern Interview Questions and Answers

Round duration - 45 minutes
Round difficulty - Medium

The first Round was held on Hackerrank and the questions were of medium difficulty based on Data Structures and Algorithms.
The time of test was 1:00 PM and it was of 45 minutes with 2 coding questions to be solved.

Q1. 
Merge Overlapping Intervals Problem Statement
Given a specified number of intervals, where each interval is represented by two integers denoting its boundaries, the task is to merge all overlapping interv...read more
Ans. 
Merge overlapping intervals and return sorted list of merged intervals.
• Identify overlapping intervals based on start and end times

• Merge overlapping intervals to form new intervals

• Sort the merged intervals in ascending order of start times
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Q2. 
Josephus Problem Statement
Consider 'N' individuals standing in a circle, numbered consecutively from 1 to N, in a clockwise direction. Initially, the person at position 1 starts counting and will skip K-...read more
Ans. 
The Josephus problem involves eliminating individuals in a circle until only one remains, based on a specific counting rule.
• Start counting from position 1, skip K-1 individuals, eliminate the Kth person, and continue until only one person remains.

• The position of the last surviving person can be determined based on the initial numbering and the value of K.

• Example: For N=5 and K=2, the last person standing is at position...read more
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Round duration - 75 minutes
Round difficulty - Medium

A google Doc was shared with us and we were supposed to write code there. 
Use of IDEs was not allowed so we had to write correct code on Google Docs which was later checked by them through online IDEs.
The Interviewer were friendly and observative and helped us through code if we made some silly error.

Q1. 
Largest Rectangle in Histogram Problem Statement
You are given an array/list HEIGHTS of length N, where each element represents the height of a histogram bar. The width of each bar is considered to be 1.
...read more
Ans. 
Compute the area of the largest rectangle that can be formed within the bounds of a given histogram.
• Iterate through the histogram bars and maintain a stack to keep track of increasing heights.

• Calculate the area of the rectangle formed by each bar as the smallest height in the stack times the width.

• Update the maximum area found so far.

• Time complexity can be optimized to O(N) using a stack-based approach.
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Q2. 
Boundary Traversal of a Binary Tree
Given a binary tree of integers, your task is to return the boundary nodes of the tree in Anti-Clockwise direction starting from the root node.
Input:
The first line ...read more
Ans. 
Return the boundary nodes of a binary tree in Anti-Clockwise direction starting from the root node.
• Traverse the left boundary nodes in top-down order

• Traverse the leaf nodes in left-right order

• Traverse the right boundary nodes in bottom-up order

• Handle duplicates in boundary nodes by including them only once
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Round duration - 60 minutes
Round difficulty - Medium

The face to face round was held on Google Meet where initially Interviewer asked a DS/Algo problem and then Later Manager Joined and asked about our resume projects in detail.
The time was 10:00 AM

Q1. 
Maximum Sum Rectangle Problem
Given an M x N matrix of integers ARR, your task is to identify the rectangle within the matrix that has the greatest sum of its elements.
Input:
The first line of input co...read more
Ans. 
Find the rectangle within a matrix with the greatest sum of elements.
• Iterate through all possible rectangles within the matrix and calculate their sums

• Use Kadane's algorithm to find the maximum sum subarray for each row combination

• Keep track of the maximum sum found so far
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Q2. 
Rotated Array Minimum Finder
You are provided with a sorted array that has undergone 'K' rotations (the exact value of 'K' is unknown). A rotation involves shifting each element of the array to the right,...read more
Ans. 
Find the minimum number in a rotated sorted array efficiently.
• Use binary search to find the minimum element in the rotated array.

• Compare mid element with the last element to determine which half to search.

• Adjust the search space based on the comparison to find the minimum element efficiently.
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Round duration - 150 minutes
Round difficulty - Medium

Q1. 
Check If Linked List Is Palindrome
Given a singly linked list of integers, determine if the linked list is a palindrome.
Explanation:
A linked list is considered a palindrome if it reads the same forwar...read more
Ans. 
Check if a given singly linked list of integers is a palindrome or not.
• Traverse the linked list to find the middle element using slow and fast pointers.

• Reverse the second half of the linked list.

• Compare the first half with the reversed second half to determine if it's a palindrome.
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Q2. 
Pair Sum Problem Statement
You are given an integer array 'ARR' of size 'N' and an integer 'S'. Your task is to find and return a list of all pairs of elements where each sum of a pair equals 'S'.
Note:
...read more
Ans. 
Find pairs of elements in an array that sum up to a given value, sorted in a specific order.
• Iterate through the array and for each element, check if the complement (S - current element) exists in a hash set.

• If the complement exists, add the pair (current element, complement) to the result list.

• Sort the result list based on the first element of each pair, and then based on the second element if the first elements are eq...read more
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Round duration - 60 minutes
Round difficulty - Medium

Q1. 
Square Root with Decimal Precision Problem Statement
You are provided with two integers, 'N' and 'D'. Your objective is to determine the square root of the number 'N' with a precision up to 'D' decimal pl...read more
Ans. 
Implement a function to find the square root of a number with a specified decimal precision.
• Implement a function that takes two integers N and D as input and returns the square root of N with precision up to D decimal places.

• Use mathematical algorithms like Newton's method to approximate the square root with the required precision.

• Ensure that the difference between the computed result and the true square root is less t...read more
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Round duration - 145 minutes
Round difficulty - Easy

The online assessment consisted of four components, a code debugging section (20 minutes), a coding test (70 minutes), a workstyles assessment (20 minutes) and a reasoning ability section (35 minutes). Code debugging questions were pretty simple and straightforward. The coding test consisted of 2 questions, first was similar to two Sum problem. Second question was similar to find the critical edges in a graph. The workstyles assessment section contained certain behavioural questions.
Reasoning ability section consisted of aptitude questions. This round was basically to check the problem solving skills of the candidate.

Q1. 
Find All Pairs Adding Up to Target
Given an array of integers ARR of length N and an integer Target, your task is to return all pairs of elements such that they add up to the Target.
Input:
The first line ...read more
Ans. 
Given an array of integers and a target, find all pairs of elements that add up to the target.
• Iterate through the array and for each element, check if the difference between the target and the element exists in a hash set.

• If it exists, then print the pair (element, target-element), else add the element to the hash set.

• If no pair is found, print (-1, -1).
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Q2. 
Bridges in a Graph Problem Statement
In an undirected graph consisting of V vertices and E edges, your task is to identify all the bridges within the graph. A bridge is an edge which, when removed, result...read more
Ans. 
Identify bridges in an undirected graph by finding edges that, when removed, increase the number of connected components.
• Use depth-first search (DFS) to find bridges in the graph.

• Keep track of discovery time and low time for each vertex during DFS.

• An edge (u, v) is a bridge if low[v] > disc[u].

• Sort and print the bridge pairs in ascending order of vertices.

• Example: If the input graph has vertices 0, 1, 2, 3, 4 and ed...read more
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Round duration - 60 minutes
Round difficulty - Medium

I was asked two coding questions. First question was related to binary tree and second question was to implement LRU cache.
I had to code both questions. The interviewer asked me the time and space complexity for both the questions.

Q1. 
Circular Array Loop Problem Statement
Given a circular array ARR of size N consisting of positive and negative integers, determine if there is a cycle present in the array. You can make movements based on...read more
Ans. 
Determine if a circular array has a cycle present, following specific movement rules.
• Iterate through the array and check for cycles following the given movement rules.

• Keep track of visited indices to detect cycles.

• Handle both clockwise and counterclockwise movements separately.

• Return 'True' if a cycle is found, 'False' otherwise.
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Q2. 
LRU Cache Implementation
Design and implement a Least Recently Used (LRU) cache data structure, which supports the following operations:
• get(key) - Return the value of the key if it exists in the cach...read more
Ans. 
Implement a Least Recently Used (LRU) cache data structure with get and put operations.
• Use a combination of a hashmap and a doubly linked list to efficiently 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.

• For get operation, return the value of th...read more
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Round duration - 60 minutes
Round difficulty - Medium

I was asked two coding questions and some conceptual questions about priority heap data structure. I was able to code the optimized approach for the first question. But second question was a little tricky for me as I had never heard it before. But I explained my approach confidently. The interviewer also helped me and finally I was able to code it.

Q1. 
Connect Ropes with Minimum Cost
Given 'N' ropes, each having different lengths, your task is to connect these ropes into one single rope. The cost to connect two particular ropes is equal to the sum of th...read more
Ans. 
Connect ropes with different lengths into one single rope with minimum cost by merging the smallest ropes first.
• Sort the lengths of ropes in ascending order.

• Merge the two smallest ropes at each step to minimize cost.

• Keep track of the total cost as you merge the ropes.

• Repeat the merging process until all ropes are connected.

• Return the total cost as the minimum cost to connect all ropes.
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Q2. 
Langford Pairing Problem Statement
Given a positive integer N, you are required to generate a list of integers of size 2N such that it contains all the integers from 1 to N, both included, twice. These in...read more
Ans. 
Generate Langford pairing for given N, return 'Valid' if correct, 'Invalid' if not.
• Generate a list of integers of size 2N with all integers from 1 to N twice.

• Arrange integers according to Langford pairing rules.

• Return 'Valid' if pairing is correct, 'Invalid' if not.

• If no valid pairing possible, return list with only -1 element.
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Round duration - 120 minutes
Round difficulty - Medium

This was an online coding, mcq and debugging round round held on Amcat platform, there were 3 sections in the test.
1)20 MCQ questions {10 involving mathematics and the other 10 on programming fundamentals}; duration:20 mins;
you cannot navigate back to a questions after moving further, so have to answer carefully
2)debugging section- it involved 7 questions which were to be completed within 20 mins, 5 of them were very easy, each question only took almost a minute to figure out the problem with the code, last 2 questions were relatively moderate and there were errors at 3-4 sections of the entire code. I was able to solve all the questions in 15 mins
3)2 Coding questions- duration:80 mins, one was moderate on string while the other one involved dynamic programming, I was able to successfully execute all the available test cases.

Q1. 
Smallest Window Problem Statement
Given two strings, S and X, your task is to find the smallest substring in S that contains all the characters present in X.
Example:
Input:
S = "abdd", X = "bd"
Outpu...read more
Ans. 
Find the smallest substring in S that contains all characters in X.
• Use a sliding window approach to find the smallest window in S containing all characters of X.

• Maintain a hashmap to keep track of characters in X and their frequencies.

• Slide the window by moving the right pointer until all characters in X are found, then move the left pointer to minimize the window size.

• Return the smallest window found.

• Example: S = 'abd...read more
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Q2. 
Minimum Sum in Matrix Problem Statement
You are given a 2D matrix 'ARR' of size 'N x 3' with integers, where 'N' is the number of rows. Your task is to compute the smallest sum achievable by selecting one...read more
Ans. 
Find the smallest sum achievable by selecting one element from each row of a 2D matrix, following certain constraints.
• Iterate through each row and find the minimum element that does not violate the constraints.

• Keep track of the minimum sum achieved by selecting elements from each row.

• Avoid selecting elements directly beneath previously selected elements.
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Round duration - 45 minutes
Round difficulty - Hard

The interview started with introduction, there were two interviewers, they both introduced themselves and then asked me to introduce myself. Then we had a brief description on my projects, and they really appreciated my projects. Then as they were more concerned with DSA part, so we moved towards solving a coding problem. It was a famous rotten oranges problem with some change in language but as I haven't seen it beforehand, I wasn't able to give them an optimal approach and had to ask for some hints, but with a certain amount of help and hints, I was able to solve the problem and successfully coded it in 5 mins. Then the interviewers went for a dry run of the algorithm and tried to run it on each and every corner case, but as my algorithm was kind of bullet proof, it successfully passed all the corner cases.
Then they went for some questions on OOPS concepts involving inheritance and we had a long discussion on virtual function and runtime polymorphism. Then the interview was ended after a Q/A round that lasted for 3-4 minutes.

Q1. 
Rotten Oranges Problem Statement
Given a grid containing oranges in three possible states:
• Value 0 - Empty cell
• Value 1 - Fresh orange
• Value 2 - Rotten orange
Every second, any fresh orange adjac...read more
Ans. 
Given a grid with fresh and rotten oranges, determine the minimum time for all oranges to become rotten.
• Create a queue to store the coordinates of rotten oranges and perform BFS to rot adjacent fresh oranges

• Track the time taken to rot all oranges and return -1 if some fresh oranges remain

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

• Example: For input grid = [[2,1,1],[1,1,0],[0,1,1]], the minimum time to...read more
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Round duration - 120 Minutes
Round difficulty - Medium

Around 4-5 pm
2 coding questions
7 debugging and output questions
20-30 aptitude questions
A section to test psychology based on various questions and situations.

Q1. 
Clone Linked List with Random Pointer Problem Statement
Given a linked list where each node has two pointers: one pointing to the next node and another which can point randomly to any node in the list or ...read more
Ans. 
Cloning a linked list with random pointers by creating new nodes rather than copying references.
• Create a deep copy of the linked list by iterating through the original list and creating new nodes with the same values.

• Update the random pointers of the new nodes by mapping the original node's random pointer index to the corresponding new node.

• Ensure the cloned linked list is an exact copy of the original by validating th...read more
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Q2. 
Next Smaller Element Problem Statement
You are provided with an array of integers ARR of length N. Your task is to determine the next smaller element for each array element.
Explanation:
The Next Smalle...read more
Ans. 
Given an array of integers, find the next smaller element for each element in the array.
• Iterate through the array from right to left and use a stack to keep track of elements.

• Pop elements from the stack until a smaller element is found or the stack is empty.

• If no smaller element is found, output -1 for that element.
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Round duration - 50 Minutes
Round difficulty - Medium

Timing - 4pm
Just asked one question based on DSA and asked to make the code modular and well indented.
Didn’t even ask for introduction.

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 minimum time to rot all fresh oranges in a grid if adjacent to rotten oranges.
• Use Breadth First Search (BFS) to simulate the rotting process of oranges.

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

• If at the end there are still fresh oranges left, return -1 as it is impossible to rot all oranges.
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Round duration - 60 Minutes
Round difficulty - Medium

Started at 4pm
Interviewer introduced himself and then asked me for a brief introduction.
Went ahead to ask 2 DSA based questions.

Q1. 
Merge k Sorted Linked Lists
You are provided with 'K' sorted linked lists, each sorted in increasing order. Your task is to merge all these lists into one single sorted linked list and return the head of ...read more
Ans. 
Merge k sorted linked lists into one single sorted linked list.
• Create a min-heap to store the heads of all k linked lists.

• Pop the smallest element from the heap and add it to the result list.

• If the popped element has a next element, push it back into the heap.

• Repeat until all elements are merged into a single sorted list.
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Q2. 
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 current direction to the path and backtrack if the path leads to a dead end.

• Return all valid paths found in alphabetical order as an ar...read more
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Round duration - 120 minutes
Round difficulty - Medium

Evening test around 5
Platform :- SHL
Environment was amazing

Q1. 
Subtree of Another Tree Problem Statement
Given two binary trees, T and S, determine whether S is a subtree of T. The tree S should have the same structure and node values as a subtree of T.
Explanation:
...read more
Ans. 
Given two binary trees T and S, determine if S is a subtree of T with the same structure and node values.
• Check if the second tree is a subtree of the first tree by comparing their structures and node values.

• Use a recursive approach to traverse both trees and check for equality.

• Handle cases where one tree is null or the values do not match.

• Return true if S is a subtree of T, false otherwise.
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Q2. 
Search in a Row-wise and Column-wise Sorted Matrix Problem Statement
You are given an N * N matrix of integers where each row and each column is sorted in increasing order. Your task is to find the positi...read more
Ans. 
Given a sorted N*N matrix, find the position of a target integer X.
• Iterate over each row and column to find the target integer X

• Utilize the sorted nature of the matrix to optimize the search process

• Return the position of X if found, else return -1 -1
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Round duration - 60 minutes
Round difficulty - Medium

1 Hour 
Afternoon

Q1. 
Intersection of Linked List Problem
You are provided with two singly linked lists containing integers, where both lists converge at some node belonging to a third linked list.
Your task is to determine t...read more
Ans. 
Find the node where two linked lists merge, return -1 if no merging occurs.
• Traverse both lists to find their lengths and the difference in lengths

• Move the pointer of the longer list by the difference in lengths

• Traverse both lists simultaneously until they meet at the merging point
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Q2. 
Problem: Pair Sum in a Binary Search Tree
Given a Binary Search Tree (BST) and an integer 'S', your task is to find all pairs of nodes within the BST that total to 'S' and return these pairs. If no such p...read more
Ans. 
Find pairs of nodes in a BST that sum up to a given value 'S'.
• Traverse the BST in-order to get a sorted list of nodes.

• Use two pointers approach to find pairs with sum 'S'.

• Keep track of visited nodes to avoid using the same node twice in a pair.
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Round duration - 60 minutes
Round difficulty - Medium

Online Round held on Chime

Q1. 
Is Binary Heap Tree Problem Statement
You are given a binary tree of integers. Your task is to determine if it is a binary heap tree or not.
Input:
The first line of input contains an integer ‘T’ denoti...read more
Ans. 
Determine if a given binary tree is a binary heap tree or not based on certain properties.
• Check if the binary tree is a complete binary tree where every level, except the last level, is completely filled and the last level is as far left as possible.

• Ensure that every parent node is greater than all its children nodes, forming a max-heap.

• If any node does not have a left or right child, it should be represented as -1 in ...read more
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Q2. 
Edit Distance Problem Statement
Given two strings S and T with lengths N and M respectively, your task is to find the "Edit Distance" between these strings.
The Edit Distance is defined as the minimum nu...read more
Ans. 
The task is to find the minimum number of operations required to convert one string into another using delete, replace, and insert operations.
• Use dynamic programming to solve the problem efficiently.

• Create a 2D array to store the edit distances between substrings of the two input strings.

• Fill up the array based on the minimum of three possible operations: insert, delete, or replace.

• The final answer will be the value at...read more
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