Insertion Sort for Singly Linked List

We have discussed Insertion Sort for arrays. In this article same for linked list is discussed.

Below is simple insertion sort algorithm for linked list.

1) Create an empty sorted (or result) list
2) Traverse the given list, do following for every node.
......a) Insert current node in sorted way in sorted or result list.
3) Change head of given linked list to head of sorted (or result) list.

The main step is (2.a) which has been covered in below post.
Sorted Insert for Singly Linked List



Below is implementation of above algorithm

C/C++

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/* C program for insertion sort on a linked list */
#include<stdio.h>
#include<stdlib.h>
  
/* Link list node */
struct Node
{
    int data;
    struct Node* next;
};
  
// Function to insert a given node in a sorted linked list
void sortedInsert(struct Node**, struct Node*);
  
// function to sort a singly linked list using insertion sort
void insertionSort(struct Node **head_ref)
{
    // Initialize sorted linked list
    struct Node *sorted = NULL;
  
    // Traverse the given linked list and insert every
    // node to sorted
    struct Node *current = *head_ref;
    while (current != NULL)
    {
        // Store next for next iteration
        struct Node *next = current->next;
  
        // insert current in sorted linked list
        sortedInsert(&sorted, current);
  
        // Update current
        current = next;
    }
  
    // Update head_ref to point to sorted linked list
    *head_ref = 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(struct Node** head_ref, struct Node* new_node)
{
    struct Node* current;
    /* Special case for the head end */
    if (*head_ref == NULL || (*head_ref)->data >= new_node->data)
    {
        new_node->next = *head_ref;
        *head_ref = new_node;
    }
    else
    {
        /* Locate the node before the point of insertion */
        current = *head_ref;
        while (current->next!=NULL &&
               current->next->data < new_node->data)
        {
            current = current->next;
        }
        new_node->next = current->next;
        current->next = new_node;
    }
}
  
/* BELOW FUNCTIONS ARE JUST UTILITY TO TEST sortedInsert */
  
/* Function to print linked list */
void printList(struct Node *head)
{
    struct Node *temp = head;
    while(temp != NULL)
    {
        printf("%d  ", temp->data);
        temp = temp->next;
    }
}
  
/* A utility function to insert a node at the beginning of linked list */
void push(struct Node** head_ref, int new_data)
{
    /* allocate node */
    struct Node* new_node = new Node;
  
    /* put in the data  */
    new_node->data  = new_data;
  
    /* link the old list off the new node */
    new_node->next = (*head_ref);
  
    /* move the head to point to the new node */
    (*head_ref)    = new_node;
}
  
  
// Driver program to test above functions
int main()
{
    struct Node *a = NULL;
    push(&a, 5);
    push(&a, 20);
    push(&a, 4);
    push(&a, 3);
    push(&a, 30);
  
    printf("Linked List before sorting \n");
    printList(a);
  
    insertionSort(&a);
  
    printf("\nLinked List after sorting \n");
    printList(a);
  
    return 0;
}

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Java

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// 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("\nLinkedList After sorting");
        list.printlist(list.head);
    }
}
  
// This code is contributed by Rishabh Mahrsee

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Python

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# Pyhton implmentation of above algorithm
  
# Node class 
class Node: 
      
    # Constructor to initialize the node object 
    def __init__(self, data): 
        self.data = data 
        self.next = None
  
# function to sort a singly linked list using insertion sort
def insertionSort(head_ref):
  
    # Initialize sorted linked list
    sorted = None
  
    # Traverse the given linked list and insert every
    # node to sorted
    current = head_ref
    while (current != None):
      
        # Store next for next iteration
        next = current.next
  
        # insert current in sorted linked list
        sorted = sortedInsert(sorted, current)
  
        # Update current
        current = next
      
    # Update head_ref to point to sorted linked list
    head_ref = sorted
    return head_ref
  
# 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())
def sortedInsert(head_ref, new_node):
  
    current = None
      
    # Special case for the head end */
    if (head_ref == None or (head_ref).data >= new_node.data):
      
        new_node.next = head_ref
        head_ref = new_node
      
    else:
      
        # Locate the node before the point of insertion 
        current = head_ref
        while (current.next != None and
            current.next.data < new_node.data):
          
            current = current.next
          
        new_node.next = current.next
        current.next = new_node
          
    return head_ref
  
# BELOW FUNCTIONS ARE JUST UTILITY TO TEST sortedInsert 
  
# Function to print linked list */
def printList(head):
  
    temp = head
    while(temp != None):
      
        print( temp.data, end = " ")
        temp = temp.next
      
# A utility function to insert a node
# at the beginning of linked list 
def push( head_ref, new_data):
  
    # allocate node
    new_node = Node(0)
  
    # put in the data 
    new_node.data = new_data
  
    # link the old list off the new node 
    new_node.next = (head_ref)
  
    # move the head to point to the new node 
    (head_ref) = new_node
    return head_ref
  
# Driver program to test above functions
  
a = None
a = push(a, 5)
a = push(a, 20)
a = push(a, 4)
a = push(a, 3)
a = push(a, 30)
  
print("Linked List before sorting ")
printList(a)
  
a = insertionSort(a)
  
print("\nLinked List after sorting ")
printList(a)
  
# This code is contributed by Arnab Kundu

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C#

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// C# program to sort link list
// using insertion sort
using System;
  
public class LinkedlistIS 
{
    public node head;
    public node sorted;
  
    public class node 
    {
        public int val;
        public 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
        {
            Console.Write(head.val + " ");
            head = head.next;
        }
    }
      
    // Driver code
    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);
        Console.WriteLine("Linked List before Sorting..");
        list.printlist(list.head);
        list.insertionSort(list.head);
        Console.WriteLine("\nLinkedList After sorting");
        list.printlist(list.head);
    }
}
  
// This code contributed by Rajput-Ji

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Output:

Linked List before sorting
30  3  4  20  5
Linked List after sorting
3  4  5  20  30

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Improved By : Rajput-Ji, andrew1234

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