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Python Program For Insertion Sort In A Singly Linked List

  • Last Updated : 18 May, 2022

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.
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 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 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 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

Output:  

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

Please refer complete article on Insertion Sort for Singly Linked List for more details!


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