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Python Program to Check whether a Singly Linked List is a Palindrome
When it is required to check if a singly linked list is a palindrome or not, methods to add an element, get the previous node and to check if a palindrome is formed are defined.
Below is a demonstration of the same −
Example
class Node:
def __init__(self, data):
self.data = data
self.next = None
class LinkedList_struct:
def __init__(self):
self.head = None
self.last_node = None
def add_elements(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 get_previous_node(self, ref_node):
curr = self.head
while (curr and curr.next != ref_node):
curr = curr.next
return curr
def check_palindrome(my_list):
beg = my_list.head
end = my_list.last_node
while (beg != end and end.next != beg):
if beg.data != end.data:
return False
beg = beg.next
end = my_list.get_previous_node(end)
return True
my_instance = LinkedList_struct()
my_input = input('Enter elements to the linked list: ').split()
for data in my_input:
my_instance.add_elements(int(data))
if check_palindrome(my_instance):
print('The linked list is palindromic in nature')
else:
print('The linked list is not palindromic in nature')Output
Enter elements to the linked list: 89 90 78 90 89 The linked list is palindromic in nature
Explanation
The ‘Node’ class is created.
Another ‘LinkedList_struct’ class with required attributes is created.
It has an ‘init’ function that is used to initialize the first element, i.e the ‘head’ to ‘None’ and last node to ‘None’.
Another method named ‘add_elements’ is defined, that is used to fetch the previous node in the linked list.
Another method named ‘get_previous_node’ is defined that is used to display the linked list data on the console.
A method named ‘check_palindrome’ is defined, that compares the first and last element, if they are not same, it determines that the list wasn’t palindromic in nature.
An object of the ‘LinkedList_struct’ class is created.
The user input is taken for the elements in the linked list.
The elements are added to the linked list.
The ‘check_palindrome’ method is called on this linked list.
Relevant output is displayed on the console.
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