/***************************************************************************
* 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: Reverse this LinkedList.
*
* Technical Details: This algorithm reverses this singly linked
* list in place, in O(n). The function uses three pointers to
* walk the list and reverse link direction between each pair
* of nodes.
*
* BTY: reversing a P-shaped LinkedList still results in a
* P-shaped LinkedList with the same head and linear section;
* only the direction of the circular portion is reversed.
*****************************************************************/
public void reverse() {
if (null == head || null == head.next) {
return;
}
Node a = head;
Node b = a.next;
Node c = b.next;
//swaps
a.next = null;
b.next = a;
a = b;
while (null != c) {
b = c;
c = c.next;
b.next = a;
a = b;
}
head = b;
}
}
public class SinglyLinkedListTest {
/**
* Test of reverse method, of class SinglyLinkedList.
*/
@Test
public void testReverse() {
System.out.println("reverse");
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]);
}
assertTrue(Arrays.equals(input, linkedList.toArray()));
linkedList.reverse();
int ndx = input.length;
for (Node n = linkedList.head; null != n; n = n.next) {
assertEquals(input[--ndx], n.data);
}
}
}
