Freecharge Interview Questions, Process, and Tips

Calculate the number of subsets of a given set

• The number of subsets of a set with n elements is 2^n

• Include the empty set and the set itself in the count

• For example, a set with 3 elements will have 2^3 = 8 subsets

Remove the kth node from the end of a linked list.

• Use two pointers, one to traverse the list and another to keep track of the kth node from the end.

• Once the first pointer reaches the end, the second pointer will be at the kth node from the end.

• Adjust the pointers to remove the kth node.

Whatsapp low level design involves messaging, encryption, media sharing, and user authentication.

• Use end-to-end encryption to secure messages

• Implement message queues for real-time message delivery

• Allow media sharing through file transfer protocols

• Use OAuth for user authentication and authorization

Find the first non-repeating character in a string

• Create a hashmap 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 frequency 1

Use an additional stack to keep track of the minimum value at each step.

• Create a stack to store the actual values.

• Create another stack to store the minimum value at each step.

• When pushing a new value, compare it with the top of the minimum stack and push the smaller value.

• When popping a value, also pop from the minimum stack.

• To get the minimum value at any step, simply peek at the top of the minimum stack.

Print even and odd numbers using different threads

• Create two threads, one for printing even numbers and one for printing odd numbers

• Use synchronization mechanisms like mutex or semaphore to ensure proper ordering of output

• Example: Thread 1 prints even numbers (2, 4, 6, ...) and Thread 2 prints odd numbers (1, 3, 5, ...)

LRU cache is a data structure that stores the most recently used items, discarding the least recently used items when full.

• Use a doubly linked list to keep track of the order of items based on their usage.

• Use a hashmap to quickly access items in the cache.

• When an item is accessed, move it to the front of the linked list to mark it as the most recently used.

Design a flight booking system for easy and efficient booking process.

• Allow users to search for flights based on destination, date, and number of passengers.

• Provide options for users to select preferred flight times, airlines, and seating preferences.

• Include secure payment processing for booking confirmation.

• Implement a user-friendly interface with clear instructions and easy navigation.

• Offer features like flight statu...read more

Convert an array of strings to a LinkedList

• Create a new LinkedList

• Iterate through the array and add each element to the LinkedList

To remove the nth node from the end of a linked list, we can use a two-pointer approach.

• Use two pointers, one moving n steps ahead of the other

• When the first pointer reaches the end, the second pointer will be at the nth node from the end

• Adjust the pointers to remove the nth node

Design a transaction system Bank Wallet.

• Implement user authentication and authorization for secure transactions

• Allow users to deposit, withdraw, and transfer funds

• Provide transaction history and balance updates

• Implement security measures such as encryption and two-factor authentication