Add to Head
by Isai Damier, Android Engineer @ Google

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/***************************************************************************
 * Author: Isai Damier
 * Title: Singly Linked List
 * Project: geekviewpoint
 * Package: datastructure
 *
 * Description: A LinkedList is a data structure that allows access
 *   to a collection of data using pointers/references. While an
 *   array can also be defined as above, LinkedLists and arrays differ
 *   in how they are stored in memory and in the operations they
 *   allow. Unlike an array that must be stored in a block of memory,
 *   the nodes of a LinkedList can be stored anywhere because each
 *   node has a reference to the node that succeeds it. Because the
 *   nodes are stored so loosely, inserting nodes into a LinkedList
 *   is easy; whereas in an array, all the succeeding elements must
 *   be shifted. Of course, insertion also means changing the size of
 *   the array, which means creating the entire array anew.
 *
 *   Perhaps the greatest beauty of LinkedList is that it allows
 *   accessing an entire sequence of nodes using only one variable:
 *   a reference to the first node in the sequence.
 *
 *   Countless operations can be performed on LinkedLists. Following
 *   are a few, ranging from the common to the very interesting.
 **************************************************************************/
 public class SinglyLinkedList {
 
  Node head = null;
  Node tail = null;
 
  /****************************************************************
   * Statement:
   *   Add the given element before the head of the list
   *   so that this element becomes the new head.
   *
   * Time Complexity of Solution:
   *   Best = Average = Worst = O(1).
   ***************************************************************/
  public void addToHead(int el) {
    head = new Node(el, head);
    if (null == tail) {
      tail = head;
    }
  }
}