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Javascript Program For Sorting Linked List Which Is Already Sorted On Absolute Values

  • Last Updated : 22 Mar, 2022

Given a linked list that is sorted based on absolute values. Sort the list based on actual values.
Examples: 

Input:  1 -> -10 
Output: -10 -> 1

Input: 1 -> -2 -> -3 -> 4 -> -5 
Output: -5 -> -3 -> -2 -> 1 -> 4 

Input: -5 -> -10 
Output: -10 -> -5

Input: 5 -> 10 
Output: 5 -> 10

Source : Amazon Interview

A simple solution is to traverse the linked list from beginning to end. For every visited node, check if it is out of order. If it is, remove it from its current position and insert it at the correct position. This is the implementation of insertion sort for linked list and the time complexity of this solution is O(n*n).
A better solution is to sort the linked list using merge sort. Time complexity of this solution is O(n Log n).
An efficient solution can work in O(n) time. An important observation is, all negative elements are present in reverse order. So we traverse the list, whenever we find an element that is out of order, we move it to the front of the linked list. 
Below is the implementation of the above idea.

ever we find an element that is out of order, we move it to the front of the linked list. 
Below is the implementation of the above idea. 

Javascript




<script>
// Javascript program to sort a linked list,
// already sorted by absolute values
 
// head of list
var head;
 
// Linked list Node
class Node
{
    constructor(d)
    {
        this.data = d;
        this.next = null;
    }
}
 
// To sort a linked list by actual values.
// The list is assumed to be sorted by
// absolute values.
function sortedList(head)
{
    // Initialize previous and current
    // nodes
    var prev = head;
    var curr = head.next;
 
    // Traverse list
    while (curr != null)
    {
        // If curr is smaller than prev, then
        // it must be moved to head
        if (curr.data < prev.data)
        {
            // Detach curr from linked list
            prev.next = curr.next;
 
            // Move current node to beginning
            curr.next = head;
            head = curr;
 
            // Update current
            curr = prev;
        }
 
        // Nothing to do if current element
        // is at right place
        else
            prev = curr;
 
        // Move current
        curr = curr.next;
    }
    return head;
}
 
/* 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(head)
{
    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(-5);
push(5);
push(4);
push(3);
push(-2);
push(1);
push(0);
document.write(
         "Original List :<br/>");
printList(head);
head = sortedList(head);
document.write(
         "Sorted list :<br/>");
printList(head);
// This code is contributed by aashish1995
</script>

Output: 

Original list :
0 -> 1 -> -2 -> 3 -> 4 -> 5 -> -5
Sorted list :
-5 -> -2 -> 0 -> 1 -> 3 -> 4 -> 5

Time Complexity: O(N)

Auxiliary Space: O(1)

Please refer complete article on Sort linked list which is already sorted on absolute values for more details!


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