ONPASSIVE Mern Stack Developer Interview Questions and Answers

Round duration - 60 minutes
Round difficulty - Medium

21 students were shortlisted from the 1st MCQ round and in this round we were asked to write the codes (function only) of 3 questions in 1 hour time.

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

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

• Handle edge cases like no fresh oranges or all oranges already rotten

• Consider using a queue to efficiently process adjacent oranges
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Q2. 
Majority Element Problem Statement
Given an array/list 'ARR' consisting of 'N' integers, your task is to find the majority element in the array. If there is no majority element present, return -1.
Exampl...read more
Ans. 
Find the majority element in an array, return -1 if no majority element exists.
• Iterate through the array and keep track of the count of each element using a hashmap.

• Check if any element's count is greater than floor(N/2) to determine the majority element.

• Return the majority element or -1 if no majority element exists.
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Q3. 
Maximum Path Sum Between Two Leaves Problem Description
You are provided with a non-empty binary tree in which each node contains a non-negative integer value. Your task is to find and return the maximum ...read more
Ans. 
Find the maximum path sum between two leaf nodes in a binary tree.
• Traverse the tree to find the maximum path sum between two leaf nodes.

• Keep track of the maximum sum found so far.

• Consider all possible paths between leaf nodes.

• Handle cases where the tree has only a single leaf node.

• Implement a recursive function to calculate the maximum path sum.
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Round duration - 60 minutes
Round difficulty - Medium

This was a technical round with DSA based questions.

Q1. 
N-th Node From The End Problem Statement
You are given a Singly Linked List of integers. The task is to find the N-th node from the end of the list.
Example:
Input:
If the given list is (1 -> -2 -&g...read more
Ans. 
Find the N-th node from the end of a Singly Linked List of integers.
• Traverse the list to find the length L of the list.

• Calculate the position of the N-th node from the beginning as L - N + 1.

• Traverse the list again to reach the calculated position and return the node's value.
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Q2. 
LCA of Binary Tree Problem Statement
You are given a binary tree consisting of distinct integers and two nodes, X and Y. Your task is to find and return the Lowest Common Ancestor (LCA) of these two nodes...read more
Ans. 
Find the Lowest Common Ancestor (LCA) of two nodes in a binary tree.
• Traverse the binary tree to find the paths from the root to nodes X and Y.

• Compare the paths to find the last common node, which is the LCA.

• Handle cases where one node is an ancestor of the other or when one node is the LCA itself.
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Q3. 
Reverse Words in a String: Problem Statement
You are given a string of length N. Your task is to reverse the string word by word. The input may contain multiple spaces between words and may have leading o...read more
Ans. 
Reverse words in a string while handling leading/trailing spaces and multiple spaces between words.
• Split the input string by spaces to get individual words

• Reverse the list of words

• Join the reversed words with a single space in between

• Handle leading/trailing spaces by stripping them before and after reversing
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Round duration - 60 minutes
Round difficulty - Easy

Technical Interview round with questions based on DSA

Q1. 
Minimum Time To Solve The Problems
Given 'N' subjects, each containing a certain number of problems, and 'K' friends, assign subjects to friends such that each subject goes to exactly one friend, maintain...read more
Ans. 
Assign subjects to friends to minimize maximum workload, find minimum time for most loaded friend.
• Sort subjects in descending order

• Assign subjects to friends one by one until all subjects are assigned

• The maximum workload will be the sum of problems assigned to the friend with the most problems

• Return the maximum workload as the minimum time required
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Q2. What is grammar in the context of compiler design?
Ans. 
Grammar in compiler design defines the syntax and structure of a programming language.
• Grammar specifies the rules for forming valid statements in a programming language.

• It consists of a set of production rules that define how valid programs can be constructed.

• There are different types of grammars such as context-free grammar, regular grammar, etc.

• Example: In C programming language, the grammar specifies that a for loop...read more
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Q3. What is a token in compiler design?
Ans. 
A token in compiler design is a basic unit of syntax that the compiler can understand and process.
• Tokens are the smallest units of a program that are meaningful to the compiler.

• Examples of tokens include keywords, identifiers, operators, and punctuation symbols.

• Tokens are generated by the lexical analysis phase of the compiler.

• Tokens are used by the parser to build the abstract syntax tree of the program.
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Round duration - 60 minutes
Round difficulty - Easy

Technical round with questions on DSA and Compiler Design mainly. He told me that you’ll be having your final HR round in some time. I knew that I was going well because he seemed to be quite satisfied with my answers.

Q1. 
Sum Root to Leaf Numbers
You are given an arbitrary binary tree consisting of N nodes, each associated with an integer value from 1 to 9. Each root-to-leaf path can be considered a number formed by concat...read more
Ans. 
Find the total sum of all root to leaf paths in a binary tree formed by concatenating node values.
• Traverse the binary tree from root to leaf nodes, keeping track of the current path sum

• Add the current path sum to the total sum when reaching a leaf node

• Use modulo (10^9 + 7) to handle large outputs
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Q2. What is a regular language?
Ans. 
A regular language is a language that can be recognized by a finite automaton.
• Regular languages can be described by regular expressions.

• Regular languages are closed under union, concatenation, and Kleene star operations.

• Examples of regular languages include the set of all strings over an alphabet that contain an even number of 'a's.
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Q3. What are NP and NP-Hard problems?
Ans. 
NP problems are decision problems that can be verified in polynomial time, while NP-Hard problems are at least as hard as the hardest problems in NP.
• NP problems can be verified in polynomial time but not necessarily solved in polynomial time.

• NP-Hard problems are at least as hard as the hardest problems in NP, but may not be in NP themselves.

• Examples of NP problems include the subset sum problem and the traveling salesm...read more
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Round duration - 30 minutes
Round difficulty - Easy

That was the round for which I’ve been waiting for hours 
She was very friendly and nice to talk to. It didn’t seem that I was talking to the HR. It was more like talking to a friend. Finally we discussed about the pay-scale and work culture in Accolite.