/***************************************************************************
* 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:
* Retrieve the kth element from this list, where
* the head is the 0th element.
*
* Time Complexity of Solution:
* Best = O(1); Worst = O(k).
*
* Technical Details: Simply count from 0 to k, meanwhile moving
* a pointer. Then return the pointer.
*****************************************************************/
public Node findKthFromHead(int k) {
if (0 > k) {
return null;
}
Node tmp = head;
int count = 0;
while (count < k && null != tmp) {
tmp = tmp.next;
count++;
}
return tmp;
}
}
public class SinglyLinkedListTest {
/**
* Test of findKthFromHead method, of class SinglyLinkedList.
*/
@Test
public void testFindKthFromHead() {
System.out.println("findKthFromHead");
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 k = 0;
assertEquals(input[k], linkedList.findKthFromHead(k).data);
k = input.length / 2;
assertEquals(input[k], linkedList.findKthFromHead(k).data);
k = input.length - 1;
assertEquals(input[k], linkedList.findKthFromHead(k).data);
k = input.length + 21;
assertEquals(null, linkedList.findKthFromHead(k));
k = -1;
assertEquals(null, linkedList.findKthFromHead(k));
}
}
