/***************************************************************************
* 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: Find the node (intersection) where the two given
* LinkedList coalesce.
*
* Technical Details: The idea is that two linked lists form a Y-shaped
* structure. The structure may be degenerated. As shown below, the use
* of a hashmap greatly reduces the complexity of the problem.
*
*
* To keep things simple, we consider t2 and t2 equal iff they both
* point to the same memory location. A broader definition of
* equality: Two nodes t2 and t1 are equal if they and their respective
* sublists are equal.
*****************************************************************/
static public Node findIntersection(Node head1, Node head2) {
Map<Node, Boolean> intersect = new HashMap<Node, Boolean>();
for (Node t = head1; null != t; t = t.next) {
intersect.put(t, true);
}
//first duplicate is intersection
for (Node t = head2; null != t; t = t.next) {
if (null != intersect.get(t)) {
return t;
}
}
return null;
}
}
public class SinglyLinkedListTest {
/**
* Test of findIntersection method, of class SinglyLinkedList.
*/
@Test
public void testFindIntersection() {
System.out.println("findIntersection");
int[] in_1 = {29, 14, 35, 2, 1, 12, 6, 7, 4, 8, 3, 0, 16, 19, 11};
int[] in_2 = {99, 78, 8, 3, 23};
SinglyLinkedList list_1 = new SinglyLinkedList();
SinglyLinkedList list_2 = new SinglyLinkedList();
for (int i = 0; i < in_1.length; i++) {
list_1.addToTail(in_1[i]);
}
assertEquals(in_1.length, list_1.size());
for (int i = 0; i < in_2.length; i++) {
list_2.addToTail(in_2[i]);
}
assertEquals(in_2.length, list_2.size());
//set intersection: list_1 and list_2 form a Y at element 6
int exp = 6;
Node found = list_1.find(exp);
assertNotNull(found);
list_2.addAllToTail(found);
assertEquals(14, list_2.size());
Node n = SinglyLinkedList.findIntersection(list_1.head, list_2.head);
assertEquals(exp, n.data);
}
}