OLX Content Moderator Interview Questions and Answers

Merge sort algorithm can be used to sort the balls in each basket and then merge the sorted baskets.

• Apply merge sort algorithm to sort the balls in each basket

• Merge the sorted baskets to get the final sorted order

• Use recursion to implement merge sort

• Time complexity of merge sort is O(nlogn)

Mutual Exclusion is a technique to ensure that only one process at a time can access a shared resource.

• It prevents race conditions and ensures data consistency.

• It can be implemented using locks, semaphores, or monitors.

• Examples include critical sections in multi-threaded programs and database transactions.

• It can lead to performance issues if not implemented efficiently.

Multithreading is the ability of a CPU to execute multiple threads concurrently. A process is an instance of a program in execution.

• Multithreading allows multiple threads to run concurrently within a single process.

• Threads share the same memory space and resources of the process they belong to.

• Processes are independent of each other and have their own memory space and resources.

• Threads are lightweight compared to proce...read more

Semaphore is a synchronization object used to control access to a shared resource.

• Semaphore is used to limit the number of threads accessing a shared resource.

• It can be used to implement critical sections and avoid race conditions.

• Semaphore can be binary or counting, depending on the number of resources available.

• Examples of semaphore in programming languages include Java's Semaphore class and Python's threading.Semaph

Wait for completion of all threads and join them into a single thread.

• Use join() method to wait for completion of each thread.

• Create a new thread and call start() method to start the execution of all threads.

• Use sleep() method to pause the execution of the current thread until all threads complete their execution.

To delete 95,000 records with limited local memory, use batch processing and delete in chunks.

• Use batch processing to delete records in chunks

• Delete records in descending order of their IDs to avoid index fragmentation

• Commit the transaction after deleting each batch to avoid long-running transactions

• Consider archiving the deleted records instead of permanently deleting them

Program in C to implement a function 'sum' that performs integer addition, float addition, and string concatenation based on the input arguments.

• Define the function 'sum' with two arguments of type 'void *'.

• Use 'if-else' statements to check the data type of the arguments.

• Perform integer addition if both arguments are of type 'int'.

• Perform float addition if both arguments are of type 'float'.

• Concatenate the strings if b...read more

SQL query for creating tables

• Use CREATE TABLE statement

• Specify table name and column names with data types

• Add constraints like primary key, foreign key, etc.

• Example: CREATE TABLE customers (id INT PRIMARY KEY, name VARCHAR(50), email VARCHAR(50))

Nested tables are tables within tables, used to organize and store complex data structures.

• Nested tables are commonly used in databases to store arrays of data within a single row of a table.

• They can also be used in programming languages to create multidimensional arrays.

• Accessing data within a nested table requires using multiple levels of indexing.

• Nested tables can improve data organization and simplify complex data

Views are virtual tables that display data from one or more tables in a database.

• Views are created using SELECT statements.

• They can be used to simplify complex queries.

• They can also be used to restrict access to sensitive data.

• Views do not store data themselves, but rather display data from underlying tables.

• Changes made to the underlying tables are reflected in the view.

I am a software developer with experience in multiple programming languages and a passion for problem-solving.

• Proficient in Java, Python, and C++

• Experience with web development using HTML, CSS, and JavaScript

• Familiarity with Agile development methodologies

• Strong problem-solving and analytical skills

• Excellent communication and teamwork abilities

Postfix expression can be evaluated using a stack data structure.

• Create an empty stack

• Scan the expression from left to right

• If the scanned character is an operand, push it onto the stack

• If the scanned character is an operator, pop two operands from the stack, perform the operation and push the result back

• Repeat until the end of the expression

• The final result is the top of the stack

In 5 years, I see myself as a senior software developer leading a team of developers to create innovative solutions.

• Leading a team of developers to create innovative solutions

• Continuing to learn and stay up-to-date with new technologies

• Contributing to the growth and success of the company

• Mentoring and coaching junior developers

• Taking on more responsibilities and challenges

Ebay is a leading e-commerce platform with a global reach and a diverse range of products.

• Ebay has a large and diverse customer base, providing opportunities to work on a variety of projects.

• The company has a strong focus on innovation and technology, which aligns with my interests and skills.

• Ebay offers a dynamic and fast-paced work environment, which I find exciting and challenging.

• The company has a strong reputation...read more

Find pair of elements in an array whose sum is equal to a given number K.

• Iterate through the array and for each element, check if K minus the element exists in the array.

• Use a hash table to store the elements and their indices for faster lookup.

• If multiple pairs exist, return any one of them.

• If no pair exists, return null or an appropriate message.

Session is maintained using session affinity or sticky sessions.

• Session affinity ensures that a user's session is always directed to the same server.

• Load balancer uses a unique identifier to route requests to the same server.

• Sticky sessions can be implemented using cookies or URL rewriting.

• Session replication can also be used to maintain session data across multiple servers.

Singleton pattern ensures only one instance of a class is created and provides a global point of access to it.

• Create a private constructor to prevent direct instantiation of the class

• Create a private static instance of the class

• Create a public static method to access the instance

• Ensure thread safety by using synchronized keyword or static initialization block

• Examples: Logger, Configuration Manager, Database Connection

Explaining abstract class, interface and multiple inheritance in PHP.

• Abstract class is a class that cannot be instantiated and can have abstract methods.

• Interface is a collection of abstract methods and constants that can be implemented by a class.

• Multiple inheritance is not possible in PHP, but can be achieved using interfaces.

• Interfaces can be implemented by multiple classes, allowing for multiple inheritance-like be

Write a stored procedure from given tables and conditions

• Identify the tables and their relationships

• Determine the conditions to be used in the stored procedure

• Write the SQL code for the stored procedure

• Test the stored procedure to ensure it returns the desired results

To increase PHP memory at run time, modify the php.ini file or use ini_set() function.

• Edit the memory_limit value in php.ini file

• Use ini_set('memory_limit', '256M') function to increase memory limit at run time

• Check for memory leaks in the code

• Use unset() function to free up memory after use

php.ini is a configuration file for PHP that allows users to customize various settings.

• Change PHP settings such as memory limit, file upload size, and error reporting

• Enable or disable extensions and modules

• Set timezone and language settings

• Configure email settings

• Control caching and session settings

Use window.location to get domain from a url in jQuery.

• Use window.location to get the full url

• Use .hostname to get the domain name

• Use .replace() to remove 'www.' if present

WAP to find smallest palindrome number larger than given number.

• Convert the given number to string and check if it is already a palindrome.

• If not, increment the number and check if it is a palindrome.

• Repeat until a palindrome number larger than the given number is found.

• Use a while loop to implement the above steps.

WAP to check if linked list elements is a palindrome without using any extra space.

• Traverse the linked list and reverse the second half of the list

• Compare the first half with the reversed second half

• Use two pointers to traverse the list, one at normal speed and other at double speed

Find the first non-repeating character in a string.

• Create a hash table to store the frequency of each character in the string.

• Iterate through the string and check the frequency of each character.

• Return the first character with a frequency of 1.

Connection pooling is a technique of reusing database connections to improve performance.

• Connection pooling helps to reduce the overhead of creating and destroying database connections.

• It maintains a pool of connections that can be reused by multiple clients.

• Connection pooling is commonly used in web applications to handle multiple requests simultaneously.

• It can be configured with parameters like maximum number of conn...read more

A singleton class in PHP is a class that can only be instantiated once.

• Create a private constructor to prevent direct instantiation

• Create a private static variable to hold the instance of the class

• Create a public static method to get the instance of the class

• Ensure that the public static method always returns the same instance

To connect to MySQL database using PHP, create a Connection class.

• Use mysqli_connect() function to establish a connection

• Pass the database credentials as parameters to the function

• Create a constructor method to initialize the connection

• Create a query method to execute SQL queries

• Close the connection using mysqli_close() method

There are three types of errors in PHP: syntax errors, runtime errors, and logical errors.

• Syntax errors occur when the code is not written correctly, such as missing semicolons or parentheses.

• Runtime errors occur during the execution of the code, such as trying to access an undefined variable.

• Logical errors occur when the code runs without errors, but produces unexpected results, such as a miscalculation in a formula.

Session in PHP allows to store user data on the server for later use.

• Session starts when a user logs in and ends when the user logs out or the session expires.

• Session data is stored on the server and identified by a unique session ID.

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

• Session can be destroyed using the session_destroy() function.

• Session can be used to store user-specific dat...read more

Find missing element in an array of elements from 0 to n-1

• Calculate sum of all elements in array and subtract from sum of n natural numbers

• Use XOR operation on all elements and n natural numbers

• Sort the array and find the missing element