SDE - 2

You are given an array of integers 'ARR' of length 'N' and an integer Target. Your task is to return all pairs of elements such that they add up to Target.

Note:

We cannot use the element at a given index twice.

Follow Up:

Try to do this problem in O(N) time complexity. 

Given a singly linked list of integers. Your task is to return the head of the reversed linked list.

For example:

The given linked list is 1 -> 2 -> 3 -> 4-> NULL. Then the reverse linked list is 4 -> 3 -> 2 -> 1 -> NULL and the head of the reversed linked list will be 4.

Follow Up :

Can you solve this problem in O(N) time and O(1) space complexity?

Ninja recently studied odd and even numbers but he is more interested in even numbers.

He has an array ‘A’ containing ‘N’ integers. He will transform this array by moving all the even numbers at the beginning of the array and all the odd numbers at the end of the array.

Output the final array after transformation. If there are multiple transformations possible for the array, output any.

Example :

N = 4
A = [ 1, 4, 3, 2 ]

Explanation : 

The even numbers are : 4, 2.
The odd numbers are : 1, 3.
The final array ‘A’ is : [ 4, 2, 1, 3 ].

 Given a system design question for booking a movie ticket more like bookmyshow.
What should be the architecture, how to handle concurrency.
What DB should be used.