Given a singly linked list, sort it using insertion sort.

Question

Accepted Answer

Insertion sort for a singly linked list.

Traverse the list and compare each node with the previous nodes
If the current node is smaller, swap it with the previous node
Repeat until the end of the list is reached
Time complexity is O(n^2)

Accepted Answer

// Java program to sort link list
// using insertion sort
 
public class LinkedlistIS 
{
    node head;
    node sorted;
 
    class node 
    {
        int val;
        node next;
 
        public node(int val) 
        {
            this.val = val;
        }
    }
 
    void push(int val) 
    {
        /* allocate node */
        node newnode = new node(val);
        /* link the old list off the new node */
        newnode.next = head;
        /* move the head to point to the new node */
        head = newnode;
    }
 
    // function to sort a singly linked list using insertion sort
    void insertionSort(node headref) 
    {
        // Initialize sorted linked list
        sorted = null;
        node current = headref;
        // Traverse the given linked list and insert every
        // node to sorted
        while (current != null) 
        {
            // Store next for next iteration
            node next = current.next;
            // insert current in sorted linked list
            sortedInsert(current);
            // Update current
            current = next;
        }
        // Update head_ref to point to sorted linked list
        head = sorted;
    }
 
    /*
     * function to insert a new_node in a list. Note that 
     * this function expects a pointer to head_ref as this
     * can modify the head of the input linked list 
     * (similar to push())
     */
    void sortedInsert(node newnode) 
    {
        /* Special case for the head end */
        if (sorted == null || sorted.val >= newnode.val) 
        {
            newnode.next = sorted;
            sorted = newnode;
        }
        else
        {
            node current = sorted;
            /* Locate the node before the point of insertion */
            while (current.next != null && current.next.val < newnode.val) 
            {
                current = current.next;
            }
            newnode.next = current.next;
            current.next = newnode;
        }
    }
 
    /* Function to print linked list */
    void printlist(node head) 
    {
        while (head != null) 
        {
            System.out.print(head.val + " ");
            head = head.next;
        }
    }
     
    // Driver program to test above functions
    public static void main(String[] args) 
    {
        LinkedlistIS list = new LinkedlistIS();
        list.push(5);
        list.push(20);
        list.push(4);
        list.push(3);
        list.push(30);
        System.out.println("Linked List before Sorting..");
        list.printlist(list.head);
        list.insertionSort(list.head);
        System.out.println("
LinkedList After sorting");
        list.printlist(list.head);
    }
}

Given a singly linked list, sort it using insertion sort.

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