O4S Interview Questions and Answers

Round duration - 90 minutes
Round difficulty - Easy

There were 22 MCQ questions of aptitude and technical based while 3 questions were of coding type.
Tips: MCQ questions were not time consuming , so try to do that questions in less time , so you will get enough time for coding questions.

Q1. 
Balanced Parentheses Check
Given a string STR consisting solely of the characters '{', '}', '(', ')', '[', and ']', determine whether the parentheses are balanced.
Input:
The first line contains an inte...read more
Ans. 
Implement a function to check if parentheses in a string are balanced.
• Use a stack to keep track of opening parentheses and pop when a closing parenthesis is encountered.

• If the stack is empty when a closing parenthesis is encountered or if there are unmatched parentheses at the end, return 'NO'.

• Ensure that all opening parentheses have a corresponding closing parenthesis in the correct order.

• Return 'YES' if all parenthes...read more
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Q2. 
Find the Next Greater Number with the Same Set of Digits
Given a string S that represents a number, determine the smallest number that is strictly greater than the original number and has the same set of ...read more
Ans. 
The task is to find the smallest number greater than the given number with the same set of digits.
• Sort the digits of the number in descending order.

• Find the first digit from the right that is smaller than the digit to its right.

• Swap this digit with the smallest digit to its right that is greater than it.

• Sort all the digits to the right of the swapped digit in ascending order to get the smallest number greater than the
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Round duration - 60 minutes
Round difficulty - Medium

My experience was very awesome , I answered all the questions , although in starting I was very nervous , so at starting interviewer help me get my confidence, interviewer was very helpful.

Q1. 
Maximum Level Sum in Binary Tree Problem Statement
Given an arbitrary binary tree consisting of N nodes, where each node is associated with a certain value, your task is to find the maximum sum for any le...read more
Ans. 
Find the maximum sum for any level in a binary tree.
• Traverse the binary tree level by level and calculate the sum for each level.

• Keep track of the maximum sum encountered so far.

• Return the maximum sum found.

• Example: For the input tree, the maximum level sum is 13 (5+6+2).
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Q2. 
Find Top K Frequent Numbers in a Stream
Given an integer array ARR and an integer K, your task is to find the K most frequent elements in ARR. Return the elements sorted in ascending order.
Example:
Inp...read more
Ans. 
Find the K most frequent elements in an integer array and return them sorted in ascending order.
• Use a hashmap to store the frequency of each element in the array.

• Use a min heap to keep track of the K most frequent elements.

• Return the elements from the min heap in ascending order.
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Round duration - 60 minutes
Round difficulty - Easy

This round was based on DSA and questions on core subjects that I had studied throughout college.

Q1. 
Vertical Sum in a Binary Tree
Given a binary tree where each node has a positive integer value, compute the vertical sum of the nodes. The vertical sum is defined as the sum of all nodes aligned along the...read more
Ans. 
Compute the vertical sum of nodes in a binary tree aligned along the same vertical line.
• Traverse the binary tree in a level order manner to calculate the vertical sum.

• Use a hashmap to store the vertical sum at each vertical level.

• Recursively traverse the tree and update the vertical sum in the hashmap.

• Output the vertical sums in the required format for each test case.
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Q2. What is TCP/IP?
Ans. 
TCP/IP is a set of protocols that governs the way data is transmitted over the internet.
• TCP/IP stands for Transmission Control Protocol/Internet Protocol.

• It is a suite of communication protocols used to connect devices on the internet.

• TCP ensures that data is reliably transmitted between devices.

• IP is responsible for addressing and routing data packets across networks.

• Examples of TCP/IP protocols include HTTP, FTP, and
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Round duration - 30 minutes
Round difficulty - Easy

Experience : Keep confidence and show them good communication skills. Previous round's performance also matters in this rounds

Round duration - 60 minutes
Round difficulty - Easy

In the interview I was asked few puzzles and few coding problems.
In the coding questions the interviewers did not ask me to write down the complete codes of the problems, they only asked me to suggest some suitable algorithms.

Q1. 
Count Set Bits Problem Statement
Given a positive integer N, find the total number of '1's in the binary representation of all the numbers from 1 to N.
You should return the result modulo 10⁹+7 as the co...read more
Ans. 
Count the total number of set bits in the binary representation of numbers from 1 to N, modulo 10^9+7.
• Iterate through numbers from 1 to N and count the set bits in their binary representation

• Use bitwise operations to count set bits efficiently

• Return the total count modulo 10^9+7 as the result
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Round duration - 45 minutes
Round difficulty - Easy

In second round of interview I was asked some hardcore programming questions on data structures since I wrote it as my area of interest. 
I was asked some puzzles as well.

Q1. 
Merge Two Sorted Arrays Problem Statement
Given two sorted integer arrays ARR1 and ARR2 of size M and N, respectively, merge them into ARR1 as one sorted array. Assume that ARR1 has a size of M + N to hol...read more
Ans. 
Merge two sorted arrays into one sorted array in place.
• Iterate from the end of both arrays and compare elements to merge in place

• Use two pointers to keep track of the current position in both arrays

• Handle cases where one array is fully merged before the other
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