OpenTap Interview Questions and Answers

Round duration - 90 minutes
Round difficulty - Medium

3 coding Questions:
1st : Easy question based on simple loop iteration
2nd :Medium level Dp question 
3rd : Medium level tree question(where we were not just required to complete the tree function but to build whole bst from 
scratch) 

It was conducted from 1:30 - 3:00 pm.
The coding platform was very good (as auto indentation and auto completion of brackets were there)
having camera on.

Q1. 
Selling Stock Problem Statement
You are given the stock prices for N days. Each day i signifies the price of a stock on that day. Your goal is to calculate the maximum profit that can be achieved by buyin...read more
Ans. 
Calculate maximum profit by buying and selling stocks on different days.
• Iterate through the stock prices and buy on the day when the price is lower than the next day's price, and sell on the day when the price is higher than the next day's price.

• Keep track of the total profit earned by summing up the differences between buying and selling prices.

• Return the total profit as the maximum profit that can be earned.
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Q2. 
Minimum Time to Burn a Binary Tree from a Leaf Node
You are given a binary tree with 'N' unique nodes, and a specific start node from where the fire will begin. The task is to determine the time in minute...read more
Ans. 
The task is to determine the time in minutes required to burn the entire binary tree starting from a given node.
• Traverse the tree from the given start node to calculate the time taken to burn the entire tree.

• Use a queue to keep track of nodes and their burning time.

• Increment the burning time for each level of nodes until the entire tree is burned.
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Round duration - 75-80 minutes
Round difficulty - Hard

This was a completely technical coding round where I was asked to solve the problems of data structures.
The codepad where i was asked to code was fine,
The interviewer was very friendly and was helpful and understanding.
I also asked him about his work and experience in the company and some other questions.

Q1. 
Matrix Maximum Path Sum Problem
Given an N*M matrix filled with integer numbers, your task is to find the maximum path sum starting from any cell in the first row and ending at any cell in the last row. Y...read more
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Round duration - 45 minutes
Round difficulty - Easy

It was held on Gmeet platform
The interviewer was very experienced person and was very nice too.
He made me comfortable by first introducing himself in a very detailed way and then asking me mine introduction
Since I feel that his internet connection was not very good so he turned off his camera but I decided not to turn off mine as in online interviews your face reviles your confidence 
the interviewer mostly asked me questions about my interests in technical field and the project that I have done

20 MCQs + 2 Coding Question

Q1. Trapping Rain Water
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Q1. Questions on time and space complexity
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Q1. General Discussion
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Q1. Find edge score of the nodes in a directed graph
Ans. 
Edge score of nodes in a directed graph
• Edge score is a measure of the importance of a node in a graph

• It is calculated by counting the number of edges that point to or from a node

• Nodes with higher edge scores are considered more important

• Edge score can be calculated using algorithms like PageRank or HITS
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Q1. Rotten oranges after every second in 2D matrix
Ans. 
Simulate rotting of oranges in a 2D matrix every second.
• Create a queue to store the coordinates of fresh oranges

• Iterate through the matrix and add the coordinates of fresh oranges to the queue

• Simulate the rotting process by iterating through the queue and rotting adjacent fresh oranges

• Keep track of the time taken for all oranges to rot

• Return -1 if there are any fresh oranges left after the simulation
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Q2. Java and Spring concepts, HTTP, HTTPS, OSI layers
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Q3. DB design for air ticket booking system
Ans. 
DB design for air ticket booking system
• Create tables for flights, passengers, bookings, and payments

• Use foreign keys to establish relationships between tables

• Include fields for flight details, passenger information, and payment details

• Consider implementing a caching mechanism for frequently accessed data
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Technical MCQs (OS, CN, etc.), 2 coding questions (medium level)

Q1. Leetcode - Rainwater Harvesting
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Q2. Leetcode - Array/String
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Q1. HR + Resume Review (Technical)
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Q2. Explain Projects/Experience
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In round 1 we could only use Java

Q1. Interviewers are very friendly. Mostly the questions were based on SQL, dsa
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Quantitative case study on cost benefit analysis of 2 types of public buses running in a city. Need to choose one of them with higher profits

Fraud detection model: 3rd party firm proposing to use thier model for fraud detection. Need to profit analysis of whether to go for it or not.

Q1. Culture fit round to understand if compatible with the company
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Q1. Minimum number of platforms required for train station
Ans. 
Minimum of two platforms are required for a train station.
• At least two platforms are needed for trains to arrive and depart simultaneously.

• Additional platforms may be required depending on the frequency of trains and passenger traffic.

• Platforms should be long enough to accommodate the longest trains that will use the station.
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Q2. Longest Palindromic substring
Ans. 
The problem is to find the longest substring that is a palindrome in a given string.
• A palindrome is a string that reads the same backward as forward.

• We can use dynamic programming to solve this problem.

• We can start by considering each character as the center of a palindrome and expand outwards to find the longest palindrome.

• We can also optimize the solution by using Manacher's algorithm which reduces the time complexit
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Q1. Sort the elements of an unsorted array
Ans. 
Use any sorting algorithm to sort the elements of an unsorted array.
• Choose an appropriate sorting algorithm based on the size of the array and the type of elements.

• Common sorting algorithms include bubble sort, insertion sort, selection sort, merge sort, quick sort, and heap sort.

• Implement the chosen algorithm in the programming language of your choice.

• Test the sorting function with various input arrays to ensure corre
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Q2. Minimum energy required to cross all the hurdles without loosing life. If any point energy becomes 0 game over. Input: [-2,-3,3,1,5]
Ans. 
Find minimum energy required to cross all hurdles without losing life.
• Calculate cumulative sum of energy required to cross each hurdle.

• Find the minimum cumulative sum and add 1 to it.

• If the minimum cumulative sum is negative, return its absolute value + 1.

• This is the minimum energy required to cross all hurdles without losing life.
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