Swap Elements
by Isai Damier

/***************************************************************************
 * 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;

  /*****************************************************************
   * Time Complexity of Solution:
   *   O(n).
   *
   * Description: Swap the given elements if they both exist. Return
   *   true for success, false for failure. If either of the inputs
   *   has duplicates, this function swaps the first occurrences only.
   *****************************************************************/
  public boolean swap(int a, int b) {
    Node A, B;//sometimes Java sucks: Should be able to declare in if.
    if (null != (A = find(a)) && null != (B = find(b))) {
      A.data = b;
      B.data = a;
      return true;
    }
    return false;
  }
}
public class SinglyLinkedListTest {

   /**
   * Test of swap method, of class SinglyLinkedList.
   */
  @Test
  public void testSwap() {
    System.out.println("swap");
    int[] input = {9, 4, 5, 2, 1, 12, 6, 7, 4, 8, 3, 0, 16, 19, 11};
    SinglyLinkedList linkedList = new SinglyLinkedList();
    for (int i = 0; i < input.length; i++) {
      linkedList.addToTail(input[i]);
    }
    linkedList.swap(9, 11);
    int[] expected = {11, 4, 5, 2, 1, 12, 6, 7, 4, 8, 3, 0, 16, 19, 9};
    assertTrue(Arrays.equals(expected, linkedList.toArray()));
    linkedList.swap(1, 7);
    int[] exp = {11, 4, 5, 2, 7, 12, 6, 1, 4, 8, 3, 0, 16, 19, 9};
    assertTrue(Arrays.equals(exp, linkedList.toArray()));
  }
}