Double elements and append zeros in linked list

Given a linked list with some two adjacent repeating nodes before a zero, task is to double the first and make next 0. After this, append all the zeros to tail.

Prerequisite: Basics of implementation of Singly Linked List

Examples :

Input : 4 -> 4 -> 0 -> 2 -> 3 -> 4 -> 
        3 -> 3 -> 0 -> 4 -> 
Output : 8-> 2-> 3-> 4-> 6-> 4-> 0-> 
         0-> 0-> 0-> 

Explanation :
First, after doubling the first element and making
second element 0 before all zeros.
8 -> 0 -> 0 -> 2 -> 3 -> 4 -> 6 -> 0 
-> 0 -> 4 ->
Next :
8 -> 6 -> 5 -> 6 -> 0 -> 0 -> 0 -> 
0 -> 0 -> 0 -> 0 -> 

Input : 0 -> 4 -> 4 -> 0 -> 3 -> 3 -> 0 
        -> 5 -> 0 -> 0 -> 6 ->
Output : 8 -> 6 -> 5 -> 6 -> 0 -> 0 -> 0 
         -> 0 -> 0 -> 0 -> 0 ->

Traverse through the linked list, and wherever there are two adjacent same data of nodes before a 0 (e.g. 4 -> 4 -> 0), then, double first element and make another as 0 (e.g. 8 -> 0 -> 0 ->). Finally, traverse the linked list and linearly point all the zeros to tail.

[sourcecode language=”Java” highlight=”109-116″]
// Java code to modify linked list
import java.util.*;

// Linked List Node
class Node
{
int data;
Node next;

// Constructor
public Node(int data)
{
this.data = data;
next = null;
}
}

// Class ro perform operations
// on linked list
class GfG
{
// Recursive function to double the one of two
// elements and make next one as 0,
// which are equal before 0
public static void changeTwoBefore0(Node head)
{
// there should be atleast three elements
// to perform required operation
if (head == null || head.next == null ||
head.next.next == null)
return;

// when two continous elements
// are same
if ((head.data == head.next.data) &&
(head.next.next.data == 0))
{

int temp = head.data;
head.data = 2*temp;
head.next.data = 0;

if (head.next.next.next != null)
head = head.next.next.next;
else
return;
}
else
head = head.next;

// recursive call to changeTwoBefore0
// for next element
changeTwoBefore0(head);
}

// function to append zeros at tail
public static Node appendZero(Node head)
{
if (head == null || head.next == null)
return head;

// Find tail node
Node tail = head;
while (tail.next != null)
tail = tail.next;
Node origTail = tail;

// Case when starting nodes have 0 values
// we need to change head in this case.
Node curr = head;
while (curr.next != null && curr.data == 0)
{
tail.next = curr;
tail = curr;
curr = curr.next;
}
head = curr;

// Now moving other 0s to end
Node prev = curr;
curr = curr.next;

// We check until original tail
while (curr != origTail)
{
// If current data is 0, append
// after tail and update tail.
if (curr.data == 0)
{
tail.next = curr;
tail = curr;
prev.next = curr.next;
}
else
prev = curr;

// We always move current
curr = curr.next;
}

// Finally making sure that linked
// list is null terminated.
tail.next = null;

return head;
}

public static Node doubleAndAppend0(Node head)
{
// Change two same nodes before 0
changeTwoBefore0(head);

// Move all 0s to end
return appendZero(head);
}

// function to display the nodes
public static void display(Node head)
{
while (head != null)
{
System.out.print(head.data + " -> ");
head = head.next;
}
}

// Driver code
public static void main(String[] args)
{

Node head = new Node(4);
head.next = new Node(4);
head.next.next = new Node(0);
head.next.next.next = new Node(2);
head.next.next.next.next = new Node(3);
head.next.next.next.next.next = new Node(4);
head.next.next.next.next.next.next = new Node(3);
head.next.next.next.next.next.next.next = new Node(3);
head.next.next.next.next.next.next.next.next = new Node(0);
head.next.next.next.next.next.next.next.next.next = new Node(4);

System.out.println("Original linked list :");
display(head);

head = doubleAndAppend0(head);

System.out.println("\nModified linked list :");
display(head);
}
}
[/sourcecode]
Output :

Original linked list :
4 -> 4 -> 0 -> 2 -> 3 -> 4 -> 3 -> 3 -> 0 -> 4 -> 
Modified linked list :
8 -> 2 -> 3 -> 4 -> 6 -> 4 -> 0 -> 0 -> 0 -> 0 -> 

Time complexity : O(n), where n is the number of nodes of linked list.



My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.




Article Tags :
Practice Tags :


Be the First to upvote.


Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.