Keystone Infrabuild Interview Questions and Answers

Good Practice

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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Q1. They will ask about your past experience and current project details in detail.
Ans. Just give the proper answer about your past experience very Convincingly and confidently.
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Q2. Few technical questions they will ask.
Ans. If you already prepared for your interview, then you can answer the basic technical questions and you will get selected.
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Q1. As this was the client round. Deep technical questions about relevant experience.
Ans. Just answer to all the questions whatever they ask in very confident manner and should have manageable comm skill to clear the client round.
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MCQ's and Coding Problem - 1 related with Java, RDBMS, JS

Q1. Basic Question on Java and Project related questions
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Q1. Introduction, Discussion regarding the roles and salary negotiation.
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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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