Skip to content
Related Articles

Related Articles

Javascript Program For Sorting A Linked List Of 0s, 1s And 2s

View Discussion
Improve Article
Save Article
Like Article
  • Last Updated : 22 Dec, 2021

Given a linked list of 0s, 1s and 2s, sort it.
Examples:

Input: 1 -> 1 -> 2 -> 0 -> 2 -> 0 -> 1 -> NULL
Output: 0 -> 0 -> 1 -> 1 -> 1 -> 2 -> 2 -> NULL

Input: 1 -> 1 -> 2 -> 1 -> 0 -> NULL 
Output: 0 -> 1 -> 1 -> 1 -> 2 -> NULL

Source: Microsoft Interview | Set 1

Following steps can be used to sort the given linked list.

  • Traverse the list and count the number of 0s, 1s, and 2s. Let the counts be n1, n2, and n3 respectively.
  • Traverse the list again, fill the first n1 nodes with 0, then n2 nodes with 1, and finally n3 nodes with 2.

Below image is a dry run of the above approach:

Below is the implementation of the above approach:

Javascript




<script>
// Javascript program to sort a 
// linked list of 0, 1 and 2
  
// Head of list
var head; 
  
// Linked list Node 
class Node 
{
    constructor(val) 
    {
        this.data = val;
        this.next = null;
    }
}
       
function sortList() 
{
    // Initialise count of 0 1 
    // and 2 as 0
    var count = [ 0, 0, 0 ];
  
    var ptr = head;
     
    /* Count total number of '0', '1' and '2'
       count[0] will store total number of
       '0's count[1] will store total number
       of '1's count[2] will store total
       number of '2's */
    while (ptr != null
    {
        count[ptr.data]++;
        ptr = ptr.next;
    }
  
    var i = 0;
    ptr = head;
  
    /* Let say count[0] = n1, count[1] = n2 and 
       count[2] = n3 now start traversing
       list from head node, 1) fill the list
       with 0, till n1 > 0 2) fill the list
       with 1, till n2 > 0 3) 
       fill the list with 2, till n3 > 0 */
    while (ptr != null
    {
        if (count[i] == 0)
            i++;
        else 
        {
            ptr.data = i;
            --count[i];
            ptr = ptr.next;
        }
    }
}
  
// Utility functions
/* Inserts a new Node at front 
   of the list. */
function push(new_data) 
{
    /* 1 & 2: Allocate the Node & 
              Put in the data */
    var new_node = new Node(new_data);
  
    // 3. Make next of new Node as head 
        new_node.next = head;
  
    // 4. Move the head to point to 
    // new Node 
    head = new_node;
}
  
// Function to print linked list 
function printList() 
{
    var temp = head;
    while (temp != null
    {
        document.write(temp.data + " ");
        temp = temp.next;
    }
    document.write("<br/>");
}
  
// Driver code
/* Constructed Linked List is
   1->2->3->4->5->6->7-> 8->8->9->null */
push(0);
push(1);
push(0);
push(2);
push(1);
push(1);
push(2);
push(1);
push(2);
  
document.write(
         "Linked List before sorting<br/>");
printList();
  
sortList();
  
document.write(
         "Linked List after sorting<br/>");
printList();
// This code is contributed by todaysgaurav
</script>

Output: 

Linked List Before Sorting
2  1  2  1  1  2  0  1  0
Linked List After Sorting
0  0  1  1  1  1  2  2  2

Time Complexity: O(n) where n is the number of nodes in the linked list. 
Auxiliary Space: O(1)

Please refer complete article on Sort a linked list of 0s, 1s and 2s for more details!


My Personal Notes arrow_drop_up
Recommended Articles
Page :

Start Your Coding Journey Now!