Blocks of the Linked List
	
	/**
	 * You are given a doubly linked list and an array of references to
nodes on
	 * the linked list. How many "blocks" are there present in the linked
list?
	 *
	 * 1 <-> 2 <-> 3 <-> 4 <-> 5 <-> 6
	 * 
	 * {2, 4, 5}
	 * 
	 * */