HackerKernel Interview Questions and Answers

Round duration - 90 minutes
Round difficulty - Medium

This round had 3 coding questions of Medium to Hard level of difficulty.

Q1. 
Balanced Parentheses Combinations
Given an integer N representing the number of pairs of parentheses, find all the possible combinations of balanced parentheses using the given number of pairs.
Explanati...read more
Ans. 
Generate all possible combinations of balanced parentheses for a given number of pairs.
• Use recursion to generate all possible combinations of balanced parentheses.

• Keep track of the number of open and close parentheses used in each combination.

• Return the valid combinations as an array of strings.
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Q2. 
Trapping Rain Water Problem Statement
You are given a long type array/list ARR of size N, representing an elevation map. The value ARR[i] denotes the elevation of the ith bar. Your task is to determine th...read more
Ans. 
Calculate the total amount of rainwater that can be trapped between given elevations in an array.
• Iterate through the array and calculate the maximum height on the left and right of each bar.

• Calculate the amount of water that can be trapped at each bar by taking the minimum of the maximum heights on the left and right.

• Sum up the trapped water at each bar to get the total trapped water for the entire array.
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Q3. 
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 adjacent to rotten oranges.
• 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 fresh oranges and return -1 if not all fresh oranges can be rotten.

• Update the grid with the new state of oranges after each second.

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

• Example...read more
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Round duration - 60 Minutes
Round difficulty - Medium

This was a standard DS/Algo round where I was given 2 questions to solve under 60 minutes. I was able to come up with the optimal approach for both the questions and then at the end of the interview I was also asked the famous Die Hard Water Puzzle.

Q1. 
Queue Using Stacks Implementation
Design a queue data structure following the FIFO (First In First Out) principle using only stack instances.
Explanation:
Your task is to complete predefined functions t...read more
Ans. 
Implement a queue using stacks following FIFO principle.
• Use two stacks to simulate a queue.

• For enQueue operation, push elements onto stack1.

• For deQueue operation, if stack2 is empty, pop all elements from stack1 and push onto stack2, then pop from stack2.

• For peek operation, if stack2 is empty, pop all elements from stack1 and push onto stack2, then return top of stack2.

• For isEmpty operation, check if both stack1 and st...read more
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Q2. 
Merge Intervals Problem Statement
You are provided with 'N' intervals, each containing two integers denoting the start time and end time of the interval.
Your task is to merge all overlapping intervals a...read more
Ans. 
Merge overlapping intervals and return sorted list of merged intervals by start time.
• Sort the intervals based on start time.

• Iterate through intervals and merge overlapping ones.

• Return the merged intervals in sorted order.
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Q3. You have a 3-liter jar and a 5-liter jar. How can you measure exactly 4 liters using these two jars?
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Round duration - 60 Minutes
Round difficulty - Medium

This round had 2 coding questions - first one related to Binary Tree and the second one was a simple question from Bit Manipulation. This was followed by some questions from OOPS.

Q1. 
Binary Tree Diameter Problem Statement
You are given a Binary Tree, and you need to determine the length of the diameter of the tree.
The diameter of a binary tree is the length of the longest path betwe...read more
Ans. 
The task is to find the diameter of a binary tree, which is the length of the longest path between any two end nodes in the tree.
• Traverse the tree to find the longest path between two nodes.

• Keep track of the maximum diameter found during traversal.

• The diameter may not necessarily pass through the root node.

• Consider both left and right subtrees while calculating the diameter.

• Example: For input 1 2 3 4 -1 5 6 -1 7 -1 -1
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Q2. 
Power of 2 Problem Statement
Determine if it is possible to reorder the digits of a given integer 'N' such that the resulting number is a power of two. The leading digit must not be zero.
Input:
The fir...read more
Ans. 
The problem involves determining if it is possible to reorder the digits of a given integer to form a power of 2.
• Iterate through all possible permutations of the digits of the given integer.

• Check if any of the permutations form a power of 2.

• Return 1 if a valid permutation is found, else return 0.
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Q3. What are some advantages of using Object-Oriented Programming (OOP)?
Ans. 
Advantages of OOP include code reusability, modularity, and easier maintenance.
• Code reusability: Objects can be reused in different parts of the program, reducing redundancy.

• Modularity: OOP allows for breaking down complex problems into smaller, more manageable parts.

• Easier maintenance: Changes to one part of the codebase do not necessarily affect other parts, making maintenance easier.

• Encapsulation: Data hiding and ab...read more
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Q4. What are access specifiers and what is their significance in Object-Oriented Programming?
Ans. 
Access specifiers define the level of access to class members in Object-Oriented Programming.
• Access specifiers include public, private, protected, and default

• Public members are accessible from outside the class

• Private members are only accessible within the class

• Protected members are accessible within the class and its subclasses

• Default access is when no access specifier is specified
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Round duration - 30 Minutes
Round difficulty - Easy

This was my last round and I hoped it to go good just like the other rounds. The interviewer was very straight to point
and professional. The interview lasted for 30 minutes.

Q1. Why should we hire you?
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