/***************************************************************************
* 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 element el before node n
*
* Time Complexity of Solution:
* Best = O(1); Worst = O(n).
*
* Technical Details: The idea here is to insert element el between node
* n and it's parent. So if node is the head of the list, el is added
* before node n and thus becomes the new head; else, we traverse the
* list looking for node n and it's parent so to add el between n
* and the parent. If node n is not on the list, then element el
* is added as the tail of the list.
*****************************************************************/
public void addBefore(int el, Node n) {
if (null == head || n.data == head.data) {
addToHead(el);
} else {
Node parent = null;
Node curr = head;
while (null != curr && curr.data != n.data) {
parent = curr;
curr = curr.next;
}
if (null != curr) {
parent.next = new Node(el, n);
} else {
addToTail(el);
}
}
}
}
public class SinglyLinkedListTest {
/**
* Test of addBefore method, of class SinglyLinkedList.
*/
@Test
public void testAddBefore() {
System.out.println("addBefore");
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]);
}
int value = 51;
linkedList.addBefore(value, linkedList.find(7));
int[] expected = {9, 4, 5, 2, 1, 12, 6, 51, 7, 4, 8, 3, 0, 16, 19, 11};
assertTrue(Arrays.equals(expected, linkedList.toArray()));
}
}
