Add first element to linked list
void push_front(int newElement) {
//1. allocate node
Node newNode = new Node();
//2. assign data element
newNode.data = newElement;
//3. assign null to the next and prev
// of the new node
newNode.next = null;
newNode.prev = null;
//4. Check the list is empty or not,
// if empty make the new node as head
if(head == null) {
head = newNode;
} else {
//5. Adjust the links and make the new
// node as head
head.prev = newNode;
newNode.next = head;
head = newNode;
}
}