LBB Little Black Book 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