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# Python Program For Insertion Sort In A Singly Linked List

We have discussed Insertion Sort for arrays. In this article we are going to discuss Insertion Sort for linked list.
Below is a simple insertion sort algorithm for a 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.

The main step is (2.a) which has been covered in the post Sorted Insert for Singly Linked List Below is implementation of above algorithm:

## Python

 `# Python implementation 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`   `# Utility Functions` `# 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 of 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 code` `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``(``"Linked List after sorting "``)` `printList(a)` `# This code is contributed by Arnab Kundu`

## Java

 `// Java implementation of the above algorithm` `// Node class` `class` `Node {` `    ``int` `data;` `    ``Node next;`   `    ``// Constructor to initialize the node object` `    ``public` `Node(``int` `data)` `    ``{` `        ``this``.data = data;` `        ``this``.next = ``null``;` `    ``}` `}`   `public` `class` `InsertionSortLinkedList {`   `    ``// Function to sort a singly linked list using insertion` `    ``// sort` `    ``public` `static` `Node insertionSort(Node head)` `    ``{`   `        ``// Initialize sorted linked list` `        ``Node sorted = ``null``;`   `        ``// Traverse the given linked list and insert every` `        ``// node to sorted` `        ``Node current = head;` `        ``while` `(current != ``null``) {`   `            ``// Store next for next iteration` `            ``Node next = current.next;`   `            ``// Insert current in sorted linked list` `            ``sorted = sortedInsert(sorted, current);`   `            ``// Update current` `            ``current = next;` `        ``}`   `        ``// Return head_ref to point to sorted linked list` `        ``return` `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())` `    ``public` `static` `Node sortedInsert(Node head,` `                                    ``Node new_node)` `    ``{` `        ``Node current = ``null``;`   `        ``// Special case for the head end` `        ``if` `(head == ``null` `|| head.data >= new_node.data) {` `            ``new_node.next = head;` `            ``head = new_node;` `        ``}` `        ``else` `{`   `            ``// Locate the node before the point of insertion` `            ``current = head;` `            ``while` `(current.next != ``null` `                   ``&& current.next.data < new_node.data) {` `                ``current = current.next;` `            ``}`   `            ``new_node.next = current.next;` `            ``current.next = new_node;` `        ``}`   `        ``return` `head;` `    ``}`   `    ``// Utility Functions`   `    ``// Function to print linked list` `    ``public` `static` `void` `printList(Node head)` `    ``{` `        ``Node temp = head;` `        ``while` `(temp != ``null``) {` `            ``System.out.print(temp.data + ``" "``);` `            ``temp = temp.next;` `        ``}` `    ``}`   `    ``// A utility function to insert a node at the beginning` `    ``// of linked list` `    ``public` `static` `Node push(Node head, ``int` `new_data)` `    ``{`   `        ``// Allocate node` `        ``Node new_node = ``new` `Node(new_data);`   `        ``// Link the old list of the new node` `        ``new_node.next = head;`   `        ``// Move the head to point to the new node` `        ``head = new_node;` `        ``return` `head;` `    ``}`   `    ``// Driver code` `    ``public` `static` `void` `main(String[] args)` `    ``{` `        ``Node a = ``null``;` `        ``a = push(a, ``5``);` `        ``a = push(a, ``20``);` `        ``a = push(a, ``4``);` `        ``a = push(a, ``3``);` `        ``a = push(a, ``30``);`   `        ``System.out.println(``"Linked List before sorting "``);` `        ``printList(a);`   `        ``a = insertionSort(a);`   `        ``System.out.println(``"\nLinked List after sorting "``);` `        ``printList(a);` `    ``}` `}`

Output:

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