Python program to create a Circular Linked List of n nodes and display it in reverse order

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Python program to create a Circular Linked List of n nodes and display it in reverse order

In this program, we create a circular linked list, then traverse the list in the reverse order and print the nodes.

ALGORITHM:

  1. Define a Node class which represents a node in the list. It has two properties data and next which will point to the next node.
  2. Define another class for creating the circular linked list, and it has two nodes: head and tail. It has two methods: add(), display() and reverse().
  3. add() will add a node to the list:
  • It first checks whether the head is null, then it will insert the node as the head.
  • Both head and tail will point to the newly added node.
  • If the head is not null, the new node will be the new tail, and new tail will point to head as it is a circular linked list.

a. display() will show all the nodes present in the list.

  • Define a new node ‘current’ that will point to the head.
  • Print current.data till current will points to head again.
  • Current will point to the next node in the list in each iteration.

a. reverse() will print the circular linked list in reverse order.

  • This method checks whether the next node to current is head which implies that, current is pointing to tail, then it will print the data of the tail node.
  • Recursively call reverse() by considering node next to current node and prints out all the nodes in reverse order starting from the tail.

PROGRAM:

  1. #Represents the node of list.  
  2. class Node:
  3.     def __init__(self,data):
  4.       self.data = data;
  5.       self.next = None;
  7. class CreateList:
  8.     #Declaring head and tail pointer as null.  
  9.     def __init__(self):
  10.       self.head = Node(None);
  11.       self.tail = Node(None);
  12.       self.head.next = self.tail;
  13.       self.tail.next = self.head;
  15.     #This function will add the new node at the end of the list.  
  16.     def add(self,data):
  17.       newNode = Node(data);
  18.       #Checks if the list is empty.  
  19.       if self.head.data is None:
  20.         #If list is empty, both head and tail would point to new node.  
  21.         self.head = newNode;
  22.         self.tail = newNode;
  23.         newNode.next = self.head;
  24.       else:
  25.         #tail will point to new node.  
  26.         self.tail.next = newNode;
  27.         #New node will become new tail.  
  28.         self.tail = newNode;
  29.         #Since, it is circular linked list tail will point to head.  
  30.         self.tail.next = self.head;
  32.     #Displays all the nodes in the list  
  33.     def display(self):
  34.         current = self.head;
  35.         if self.head is None:
  36.           print(“List is empty”);
  37.           return;
  38.         else:
  39.             #Prints each node by incrementing pointer.  
  40.             print(current.data),
  41.             while(current.next != self.head):
  42.                 current = current.next;
  43.                 print(current.data),
  45.     #Reverse the order of the nodes present in the list.  
  46.     def reverse(self, current):
  47.         #Checks if the next node is head, if yes then prints it.  
  48.         if(current.next == self.head):
  49.             print(current.data),
  50.             return;
  51.         #Recursively calls the reverse function  
  52.         self.reverse(current.next);
  53.         print(current.data),
  56. class CircularLinkedList:
  57.     cl = CreateList();
  58.     #Adds data to the list  
  59.     cl.add(1);
  60.     cl.add(2);
  61.     cl.add(3);
  62.     cl.add(4);
  63.     cl.add(5);
  64.     cl.add(6);
  65.     print(“Original List: “);
  66.     cl.display();
  67.     print(“\nReversed List: “);
  68.     #Print reversed list  
  69.     cl.reverse(cl.head);

Output:

Original List: 
1 2 3 4 5 6
Reversed List: 
6 5 4 3 2 1
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