Openhouse Interview Questions and Answers

Round duration - 45 minutes
Round difficulty - Easy

This was a test where 2 coding questions were to be solved in 45 minutes.

Q1. 
Excel Column Number Conversion
Given a column title as it appears in an Excel sheet, your task is to return its corresponding column number.
Example:
Input:
S = "AB"
Output:
28
Explanation:
The seq...read more
Ans. 
Convert Excel column title to corresponding column number.
• Iterate through the characters in the input string from right to left

• Calculate the value of each character based on its position and multiply by 26^index

• Sum up the values to get the final column number
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Q2. 
Check Permutation Problem
Determine if two given strings, str1 and str2, are permutations of each other.
Explanation:
Two strings are permutations of each other if the characters of one string can be re...read more
Ans. 
Check if two strings are permutations of each other.
• Create character frequency maps for both strings.

• Compare the frequency maps to check if they are permutations.

• Handle edge cases like empty strings or strings of different lengths.
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Round duration - 60 minutes
Round difficulty - Easy

This was a written coding test with 2 coding questions to be solved in 60 minutes.

Q1. 
Find Missing Number In String Problem Statement
You have a sequence of consecutive nonnegative integers. By appending all integers end-to-end, you formed a string S without any separators. During this pro...read more
Ans. 
Given a string of consecutive nonnegative integers with one missing number, find the missing integer.
• Iterate through the string to find the missing number by checking the consecutive integers.

• If there is more than one missing number, all integers are present, or the string is invalid, return -1.

• Handle cases where the missing number is at the beginning or end of the sequence.

• Consider edge cases such as single-digit numb
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Q2. 
First Non-Repeating Character Problem Statement
You are given a string consisting of English alphabet characters. Your task is to identify and return the first character in the string that does not repeat...read more
Ans. 
The task is to find the first non-repeating character in a string, or return the first character if all characters repeat.
• Iterate through the string to count the frequency of each character

• Find the first character with a frequency of 1, or return the first character if no such character exists

• Handle both uppercase and lowercase characters separately

• Use a hashmap to store character frequencies efficiently
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Round duration - 60 minutes
Round difficulty - Medium

Technical interview round with questions around PHP and DBMS.

Q1. What is connection pooling?
Ans. 
Connection pooling is a technique used to manage a pool of database connections to improve performance and efficiency.
• Connection pooling reduces the overhead of opening and closing database connections for each request.

• It allows multiple clients to reuse a pre-established set of connections to the database.

• Connection pooling helps in improving the scalability and performance of applications by efficiently managing data...read more
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Q2. How would you create a singleton design pattern in PHP 5?
Ans. 
To create a singleton design pattern in PHP 5, use a private static variable to store the instance and a static method to retrieve it.
• Create a private static variable to store the instance of the class.

• Create a private constructor to prevent outside instantiation of the class.

• Create a static method to check if an instance already exists and return it, or create a new instance if it doesn't.
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Q3. Can you write code to connect PHP to MySQL?
Ans. 
Yes, PHP can be used to connect to MySQL by using MySQLi or PDO extensions.
• Use MySQLi extension to connect PHP to MySQL

• Use PDO extension to connect PHP to MySQL

• Example using MySQLi: $conn = new mysqli($servername, $username, $password, $dbname);

• Example using PDO: $conn = new PDO('mysql:host=$servername;dbname=$dbname', $username, $password);
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Q4. What are the different types of errors in PHP?
Ans. 
Different types of errors in PHP include syntax errors, runtime errors, and logical errors.
• Syntax errors: Occur when there is a mistake in the code syntax, preventing the script from running.

• Runtime errors: Happen during script execution, such as division by zero or calling a function that does not exist.

• Logical errors: Difficult to detect as the code runs without errors, but produces incorrect results.

• Fatal errors: St...read more
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Q5. How does session management work in PHP?
Ans. 
Session management in PHP involves storing user data on the server to maintain state between multiple requests.
• Sessions are started using session_start() function in PHP.

• Session data is stored on the server and a unique session ID is sent to the client's browser.

• Session variables can be set, accessed, and unset using $_SESSION superglobal array.

• Sessions can be destroyed using session_destroy() function.
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Round duration - 60 minutes
Round difficulty - Medium

Technical round where the interviewer asked me questions based on data structures , algorithms and load balancer and session management.

Q1. 
Pair Sum Problem Statement
You are given an integer array 'ARR' of size 'N' and an integer 'S'. Your task is to find and return a list of all pairs of elements where each sum of a pair equals 'S'.
Note:
...read more
Ans. 
Find pairs of elements in an array that sum up to a given value, sorted in a specific order.
• Iterate through the array and use a hashmap to store the difference between the target sum and each element.

• Check if the difference exists in the hashmap, if so, add the pair to the result list.

• Sort the result list based on the criteria mentioned in the problem statement.
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Q2. 
Next Smallest Palindrome Problem Statement
Find the next smallest palindrome strictly greater than a given number 'N' represented as a string 'S'.
Explanation:
You are given a number in string format, a...read more
Ans. 
Find the next smallest palindrome greater than a given number represented as a string.
• Convert the string number to an integer for comparison.

• Increment the number until a palindrome greater than the input is found.

• Handle cases where the input is already a palindrome or has leading zeros.

• Return the next greater palindrome as a string.
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Round duration - 60 minutes
Round difficulty - Medium

Technical round where the interviewer asked me questions based on data structures , design patterns and php.

Q1. 
Check If Linked List Is Palindrome
Given a singly linked list of integers, determine if the linked list is a palindrome.
Explanation:
A linked list is considered a palindrome if it reads the same forwar...read more
Ans. 
Check if a given singly linked list of integers is a palindrome.
• Create a function to reverse the linked list.

• Use slow and fast pointers to find the middle of the linked list.

• Compare the first half of the linked list with the reversed second half to determine if it's a palindrome.
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Q2. Can you explain the implementation of the Singleton Design pattern?
Ans. 
Singleton Design pattern ensures a class has only one instance and provides a global point of access to it.
• Ensure the class has a private static instance variable.

• Provide a public static method to access the instance.

• Make the constructor private to prevent instantiation from outside the class.

• Lazy initialization can be used to create the instance only when needed.

• Thread safety considerations may be necessary in a multi
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Round duration - 60 minutes
Round difficulty - Medium

Technical round where the interviewer asked me questions based on Javascript, dbms, oops concepts and php.

Q1. Write a stored procedure to join two tables.
Ans. 
A stored procedure to join two tables in a database.
• Use the JOIN keyword to combine rows from two or more tables based on a related column between them.

• Specify the columns to be selected from each table in the SELECT statement.

• Use the ON keyword to specify the join condition.

• Consider using INNER JOIN, LEFT JOIN, RIGHT JOIN, or FULL JOIN based on the desired result.

• Test the stored procedure with sample data to ensure it
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Q2. What is the difference between an abstract class and an interface in Object-Oriented Programming?
Ans. 
Abstract class can have both abstract and non-abstract methods, while interface can only have abstract methods.
• Abstract class can have constructors, fields, and methods, while interface cannot have any implementation.

• A class can only extend one abstract class, but can implement multiple interfaces.

• Abstract classes are used to define common characteristics among subclasses, while interfaces are used to define a contract...read more
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Q3. How can you extract the domain name from a URL using jQuery?
Ans. 
Use jQuery to extract domain name from a URL
• Use the 'a' element to create a temporary link with the URL

• Access the 'hostname' property of the link to get the domain name

• Use regular expressions to extract the domain name from the URL
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Q4. What are closures in JavaScript?
Ans. 
Closures in JavaScript are functions that have access to variables from their outer scope even after the outer function has finished executing.
• Closures allow functions to access variables from their parent function even after the parent function has finished executing.

• They are created whenever a function is defined within another function.

• Closures are commonly used to create private variables and functions in JavaScrip...read more
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Round duration - 60 minutes
Round difficulty - Easy

This was a coding test where we had to solve 2 coding questions in 60 minutes.

Q1. 
Buy and Sell Stock Problem Statement
Imagine you are Harshad Mehta's friend, and you have been given the stock prices of a particular company for the next 'N' days. You can perform up to two buy-and-sell ...read more
Ans. 
The task is to determine the maximum profit that can be achieved by performing up to two buy-and-sell transactions on a given set of stock prices.
• Iterate through the array of stock prices to find the maximum profit that can be achieved by buying and selling stocks.

• Keep track of the maximum profit that can be obtained by performing up to two transactions.

• Consider all possible combinations of buying and selling stocks to...read more
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Q2. 
Subsequences of String Problem Statement
You are provided with a string 'STR' that consists of lowercase English letters ranging from 'a' to 'z'. Your task is to determine all non-empty possible subsequen...read more
Ans. 
Generate all possible subsequences of a given string.
• Use recursion to generate all possible subsequences by including or excluding each character in the string.

• Maintain a current index to keep track of the characters being considered.

• Append the current character to each subsequence generated so far.

• Recursively call the function with the next index to include the next character in subsequences.
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Round duration - 60 minutes
Round difficulty - Easy

This was a technical round where the interviewer asked me questions related to OS and Java.

Q1. What is the critical section problem?
Ans. 
The critical section problem is a synchronization issue in concurrent programming where multiple processes access shared resources.
• Critical section is a code segment that accesses shared resources and must be executed by only one process at a time.

• The goal is to prevent race conditions and ensure mutual exclusion.

• Solutions include using locks, semaphores, and mutex to control access to critical sections.

• Example: Multip...read more
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Q2. How can we create a thread in Java?
Ans. 
A thread in Java can be created by extending the Thread class or implementing the Runnable interface.
• Extend the Thread class and override the run() method

• Implement the Runnable interface and provide the implementation for the run() method

• Start the thread using the start() method
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Round duration - 30 minutes
Round difficulty - Easy

Typical HR round with behavioral questions.