O3 Hire Interview Questions and Answers

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 - 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.