EatClub Interview Questions and Answers

Regex for email validation

• Start with a string of characters followed by @ symbol

• Followed by a string of characters and a period

• End with a string of characters with a length of 2-6 characters

• Allow for optional subdomains separated by periods

• Disallow special characters except for . and _ in username

Print prime numbers in a given range and optimize the solution.

• Use Sieve of Eratosthenes algorithm to generate prime numbers efficiently

• Start with a boolean array of size n+1, mark all as true

• Loop through the array and mark all multiples of each prime as false

• Print all the indexes that are still marked as true

Find angle between hour and minute hand in a clock given the time.

• Calculate the angle made by the hour hand with respect to 12 o'clock position

• Calculate the angle made by the minute hand with respect to 12 o'clock position

• Find the difference between the two angles and take the absolute value

• If the angle is greater than 180 degrees, subtract it from 360 degrees to get the smaller angle

To un-hash a string, use a reverse algorithm to convert the hash back to the original string.

• Create a reverse algorithm that takes the hash as input and outputs the original string

• Use the same logic as the hash function but in reverse order

• If the hash function used a specific algorithm, use the inverse of that algorithm to un-hash the string

Print only the leaf nodes of a doubly linked tree.

• Traverse the tree and check if a node has no children and both left and right pointers are null.

• If yes, then it is a leaf node and print it.

• If no, then continue traversing the tree.

• Use recursion to traverse the tree in a depth-first manner.

LRU page replacement algorithm is used to replace the least recently used page in memory with a new page.

• LRU stands for Least Recently Used

• It is a cache eviction algorithm

• It is used to manage memory in operating systems

• It works by keeping track of the pages that are used recently and the ones that are not

• When a new page is to be loaded into memory, the algorithm checks which page has not been used for the longest time

Reverse m nodes and leave n nodes in a linked list till the end.

• Traverse the linked list till m nodes and reverse them

• Traverse n nodes and continue reversing m nodes

• Repeat the above step till the end of the linked list

• Handle edge cases like m or n being greater than the length of the linked list

Inorder traversal is a way of visiting all nodes in a binary tree by visiting the left subtree, then the root, and then the right subtree.

• Start at the root node

• Traverse the left subtree recursively

• Visit the root node

• Traverse the right subtree recursively

• Repeat until all nodes have been visited

Inorder traversal of a tree without recursion

• Create an empty stack and initialize current node as root

• Push the current node to stack and set current = current.left until current is NULL

• If current is NULL and stack is not empty, pop the top item from stack, print it and set current = popped_item.right

• Repeat step 2 and 3 until stack is empty

Find the triplicate number in an array of duplicates.

• Iterate through the array and keep track of the frequency of each number.

• Return the number that appears three times.

• If no number appears three times, return null.

Explanation of search algorithms with their space and time complexities.

• Linear Search - O(n) time complexity, O(1) space complexity

• Binary Search - O(log n) time complexity, O(1) space complexity

• Jump Search - O(√n) time complexity, O(1) space complexity

• Interpolation Search - O(log log n) time complexity, O(1) space complexity

• Exponential Search - O(log n) time complexity, O(1) space complexity

• Fibonacci Search - O(log n)

Find the most repeated number in an array of length n with numbers 1-n.

• Create a dictionary to store the count of each number in the array

• Iterate through the array and update the count in the dictionary

• Find the key with the highest count in the dictionary

GET is used to retrieve data from a server, while POST is used to send data to a server.

• GET requests are idempotent, meaning they can be repeated without changing the result

• POST requests are not idempotent and can have side effects on the server

• GET requests can be cached by the browser, while POST requests cannot

• GET requests have limitations on the amount of data that can be sent, while POST requests have no limitation...read more

Session in PHP is a way to store and retrieve data for a user across multiple requests.

• Sessions are used to maintain user-specific data on the server side.

• A session is created for each user and is identified by a unique session ID.

• Session data can be stored in server files or in a database.

• Session variables can be accessed and modified throughout the user's session.

• Sessions can be used to implement features like user a

Session ID is stored in PHP as a cookie or a query parameter.

• Session ID can be stored as a cookie in the client's browser.

• Session ID can also be stored as a query parameter in the URL.

• The server identifies the client by retrieving the session ID from the cookie or query parameter.

• The session ID is then used to retrieve the corresponding session data stored on the server.

• The server can also use other methods like IP add

A cookie in PHP is a small piece of data stored on the client's computer. It has a size limit and an expiry date.

• A cookie is used to store information on the client's computer for future use.

• In PHP, cookies are set using the setcookie() function.

• The size of a cookie is limited to 4KB.

• Cookies can have an expiry date, after which they are no longer valid.

• The expiry date can be set using the 'expires' parameter in the set...read more

Triggers in MySQL are database objects that are automatically executed in response to specified events.

• Triggers are used to enforce business rules, maintain data integrity, and automate tasks.

• They can be defined to execute before or after an INSERT, UPDATE, or DELETE operation.

• Triggers can be written in SQL or in a programming language like PL/SQL.

• Examples of trigger events include inserting a new record, updating a re...read more

Yes, a constructor can be declared as private.

• Declaring a constructor as private restricts its accessibility to only the class itself.

• This can be useful in scenarios where you want to control the creation of objects of that class.

• Private constructors are commonly used in singleton design pattern implementations.

• Example: private constructor in a singleton class:

• class Singleton { private Singleton() {} }

Indexing in MySQL improves the performance of database queries by creating a data structure that allows for faster data retrieval.

• Indexes are created on one or more columns of a table.

• They help in speeding up the search, sorting, and joining of data.

• Indexes can be created using the CREATE INDEX statement.

• Common types of indexes include B-tree, hash, and full-text indexes.

• Indexes should be used judiciously as they consu...read more

Change binary tree to make parent node the sum of root nodes

• Traverse the tree in post-order

• For each node, update its value to the sum of its children

• Return the updated root node

Reverse a linkedlist by changing the direction of pointers.

• Iterate through the linkedlist and change the direction of pointers.

• Keep track of previous, current and next nodes.

• Set the next pointer of current node to previous node.

• Move to next node and repeat until end of list is reached.

Rearrange an array of positive and negative numbers with positive numbers on the left and negative numbers on the right.

• Create two empty arrays, one for positive numbers and one for negative numbers

• Loop through the original array and add positive numbers to the positive array and negative numbers to the negative array

• Concatenate the positive and negative arrays to create the rearranged array

String pool is a cache of string literals in memory. Garbage collection frees up memory by removing unused objects.

• String pool is a cache of string literals in memory

• Strings are immutable and can be shared among multiple objects

• Garbage collection removes unused objects to free up memory

• String objects that are no longer referenced are eligible for garbage collection

Process vs Thread differences and synchronization, deadlock examples

• Process is an instance of a program while thread is a subset of a process

• Processes are independent while threads share the same memory space

• Synchronization is used to coordinate access to shared resources

• Deadlock occurs when two or more threads are blocked waiting for each other to release resources

• Examples of synchronization include mutex, semaphore, ...read more