Digital Specialist Engineer

Ninjas is practicing problems on the linked list. He came across a problem in which he has given a linked list of ‘N’ nodes and two integers, ‘LOW’ and ‘HIGH’. He has to return the linked list ‘HEAD’ after reversing the nodes between ‘LOW’ and ‘HIGH’, including the nodes at positions ‘LOW’ and ‘HIGH’.

You are given a Singly Linked List of integers. Return true if it has a cycle, else return false.

A cycle occurs when a node's next points back to a previous node in the list.

Example:

In the given linked list, there is a cycle, hence we return true.

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. 

Suppose you have two tables in a database, "customers" and "orders". The "customers" table has a primary key "customer_id", and the "orders" table has a foreign key "customer_id" that references the "customers" table. Write a SQL query to retrieve the names of all customers who have placed an order.