1) Design patterns (Singleton, Factory)

2) Basic OOP concepts

3) Data structures(Stacks, queues and linked lists) basic iterative/recursive algorithms

Find the intersection of two lists, get all the leaf nodes of a binary tree.

Form the index of a book

How to get 45 mins using two ropes

Logic question: You have two strings that both take an hour total to burn. Using these two strings and a lighter, determine when 45 minutes has passed.

If you have 2 ropes and they both burn for an hour if lit on one end what is the most effective way to measure 45 min

find missing number, given that one number is missing from 1 to 100, how to find it

Count the number of bits of 1 in a integer. There is a classic solution link

Explain and draw an example of flyweight design pattern link