# Find Kth from Tailby Isai Damier, Android Engineer @ Google

```/***************************************************************************
* Author: Isai Damier
* 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.
**************************************************************************/

Node tail = null;

/*****************************************************************
* Statement:
*   Retrieve the node that is k units from the tail.
*
* Time Complexity of Solution:
*   Best = O(1); Worst = O(n).
*
* Technical Details: The imagery is to get a poll, k units long.
*   Place the poll along the LinkedList so that one end
*   (labeled X) of the poll is by the head node and one end
*   (labeled Y) is by some other node called tmp. Now slide the
*   poll along the LinkedList, until the end labeled Y reaches
*   the tail. At this point, return the node by X.
*****************************************************************/
public Node findKthFromTail(int k) {
if (0 > k) {
return null;
}
//count k units from the head.
int count = 0;
while (count < k && null != tmp) {
tmp = tmp.next;
count++;
}
//if the LinkedList does not contain k elements, return null
if (count < k || null == tmp) {
return null;
}

//keeping tab on the kth element from tmp, slide tmp until
//tmp equals tail. Then return the kth element.
while (null != tmp.next) {
tmp = tmp.next;
kth = kth.next;
}
return kth;
}
}```
```public class SinglyLinkedListTest {

/**
* Test of findKthFromTail method, of class SinglyLinkedList.
*/
@Test
public void testFindKthFromTail() {
System.out.println("findKthFromTail");
int[] input = {9, 4, 5, 2, 1, 12, 6, 7, 4, 8, 3, 0, 16, 19, 11};
for (int i = 0; i < input.length; i++) {
}
int k = 0;
int last = input.length - 1;