Python Program to Convert Singly Linked List to Circular List

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This is a Python program to convert a given singly linked list to a circular list.

Problem Description

The program creates a singly linked list and converts it into a circular list.

Problem Solution

1. Create a class Node with instance variables data and next.
2. Create a class LinkedList with instance variables head and last_node.
3. The variable head points to the first element in the single linked list while last_node points to the last.
4. Define method append to append data items to the list.
5. Define function convert_to_circular which takes a singly linked list as argument.
6. The function convert_to_circular converts the list passed into a circular list by making the last node point to the first.
7. Define function print_last_node_points_to to display what the last node of the passed linked list points to.
8. Create an instance of LinkedList, append data to it and convert it to a circular list.

Program/Source Code

Here is the source code of a Python program to convert a singly linked list to a circular list. The program output is shown below.

class Node:
    def __init__(self, data):
        self.data = data
        self.next = None
 
 
class LinkedList:
    def __init__(self):
        self.head = None
        self.last_node = None
 
    def append(self, data):
        if self.last_node is None:
            self.head = Node(data)
            self.last_node = self.head
        else:
            self.last_node.next = Node(data)
            self.last_node = self.last_node.next
 
 
def convert_to_circular(llist):
    if llist.last_node:
        llist.last_node.next = llist.head
 
 
def print_last_node_points_to(llist):
    last = llist.last_node
    if last is None:
        print('List is empty.')
        return
    if last.next is None:
        print('Last node points to None.')
    else:
        print('Last node points to element with data {}.'.format(last.next.data))
 
 
a_llist = LinkedList()
 
data_list = input('Please enter the elements in the linked list: ').split()
for data in data_list:
    a_llist.append(int(data))
 
print_last_node_points_to(a_llist)
 
print('Converting linked list to a circular linked list...')
convert_to_circular(a_llist)
 
print_last_node_points_to(a_llist)
Program Explanation

1. An instance of LinkedList is created.
2. The user is prompted to enter the data items for the list.
3. The singly linked list is converted to a circular list by passing the list to the function convert_to_circular.
4. The user is shown to what the last node of the list points to before and after the conversion by calling the function print_last_node_points_to.

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Runtime Test Cases
Case 1:
Please enter the elements in the linked list: 7 2 3 40 1
Last node points to None.
Converting linked list to a circular linked list...
Last node points to element with data 7.
 
Case 2:
Please enter the elements in the linked list: 3
Last node points to None.
Converting linked list to a circular linked list...
Last node points to element with data 3.
 
Case 3:
Please enter the elements in the linked list: 1 2
Last node points to None.
Converting linked list to a circular linked list...
Last node points to element with data 1.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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