# Circular Single Linked List in Python

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This is a Python program to demonstrate a circular single linked list.

Problem Description

The program creates a circular single linked list and presents the user with a menu to perform various operations on the list.

Problem Solution

1. Create a class Node with instance variables data and next.
3. The variable head points to the first element in the circular single linked list.
4. Define methods get_node, get_prev_node, insert_after, insert_before, insert_at_beg, insert_at_end, remove and display.
5. get_node takes an index as argument and traverses the list from the first node that many times to return the node at that index. It stops if it reaches the first node again.
6. get_prev_node takes a reference node as argument and returns the previous node.
7. The methods insert_after and insert_before insert a node after or before some reference node in the list.
8. The methods insert_at_beg and insert_at_end insert a node at the first or last position of the list.
9. The method remove takes a node as argument and removes it from the list.
10. The method display traverses the list from the first node and prints the data of each node. It stops when it reaches the first node again.
11. Create an instance of CircularLinkedList and present the user with a menu to perform operations on the list.

Program/Source Code

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

```class Node:
def __init__(self, data):
self.data = data
self.next = None

def __init__(self):

def get_node(self, index):
return None
for i in range(index):
current = current.next
return None
return current

def get_prev_node(self, ref_node):
return None
while current.next != ref_node:
current = current.next
return current

def insert_after(self, ref_node, new_node):
new_node.next = ref_node.next
ref_node.next = new_node

def insert_before(self, ref_node, new_node):
prev_node = self.get_prev_node(ref_node)
self.insert_after(prev_node, new_node)

def insert_at_end(self, new_node):
new_node.next = new_node
else:

def insert_at_beg(self, new_node):
self.insert_at_end(new_node)

def remove(self, node):
else:
prev_node = self.get_prev_node(node)
prev_node.next = node.next

def display(self):
return
while True:
print(current.data, end = ' ')
current = current.next
break

print('insert <data> after <index>')
print('insert <data> before <index>')
print('insert <data> at beg')
print('insert <data> at end')
print('remove <index>')
print('quit')

while True:
print('The list: ', end = '')
a_cllist.display()
print()
do = input('What would you like to do? ').split()

operation = do.strip().lower()

if operation == 'insert':
data = int(do)
position = do.strip().lower()
new_node = Node(data)
suboperation = do.strip().lower()
if suboperation == 'at':
if position == 'beg':
a_cllist.insert_at_beg(new_node)
elif position == 'end':
a_cllist.insert_at_end(new_node)
else:
index = int(position)
ref_node = a_cllist.get_node(index)
if ref_node is None:
print('No such index.')
continue
if suboperation == 'after':
a_cllist.insert_after(ref_node, new_node)
elif suboperation == 'before':
a_cllist.insert_before(ref_node, new_node)

elif operation == 'remove':
index = int(do)
node = a_cllist.get_node(index)
if node is None:
print('No such index.')
continue
a_cllist.remove(node)

elif operation == 'quit':
break```
Program Explanation

1. An instance of CircularLinkedList is created.
2. The user is presented with a menu to perform various operations on the list.
3. The corresponding methods are called to perform each operation.

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Runtime Test Cases
```Case 1:
insert <data> after <index>
insert <data> before <index>
insert <data> at beg
insert <data> at end
remove <index>
quit
The list:
What would you like to do? insert 7 at beg
The list: 7
What would you like to do? insert 1 before 0
The list: 7 1
What would you like to do? insert 10 after 0
The list: 7 10 1
What would you like to do? insert 3 at end
The list: 7 10 1 3
What would you like to do? remove 2
The list: 7 10 3
What would you like to do? remove 0
The list: 10 3
What would you like to do? quit

Case 2:
insert <data> after <index>
insert <data> before <index>
insert <data> at beg
insert <data> at end
remove <index>
quit
The list:
What would you like to do? insert 1 at beg
The list: 1
What would you like to do? insert 3 after 2
No such index.
The list: 1
What would you like to do? remove 1
No such index.
The list: 1
What would you like to do? insert 6 after 0
The list: 1 6
What would you like to do? remove 0
The list: 6
What would you like to do? quit```

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