Python Program To Check Whether The Length Of Given Linked List Is Even Or Odd

Last Updated : 15 Feb, 2023

Given a linked list, the task is to make a function which checks whether the length of the linked list is even or odd.
Examples:

Input : 1->2->3->4->NULL Output : Even  Input : 1->2->3->4->5->NULL Output : Odd

Method 1: Count the codes linearly
Traverse the entire Linked List and keep counting the number of nodes. As soon as the loop is finished, we can check if the count is even or odd. You may try it yourself.
Method 2: Stepping 2 nodes at a time
Approach:

1. Take a pointer and move that pointer two nodes at a time 2. At the end, if the pointer is NULL then length is Even, else Odd.

Python3

# Python program to check length  # of a given linklist  # Defining structure  class Node:      def __init__(self, d):         self.data = d         self.next = None         self.head = None      # Function to check the length      # of linklist      def LinkedListLength(self):         while (self.head != None and                 self.head.next != None):              self.head = self.head.next.next                      if(self.head == None):             return 0         return 1          # Push function      def push(self, info):              # Allocating node          node = Node(info)       # Next of new node to head          node.next = (self.head)       # head points to new node          (self.head) = node   # Driver code  head = Node(0)       # Adding elements to Linked List  head.push(4)  head.push(5)  head.push(7)  head.push(2)  head.push(9)  head.push(6)  head.push(1)  head.push(2)  head.push(0)  head.push(5)  head.push(5)  check = head.LinkedListLength()      # Checking for length of  # linklist  if(check == 0):     print("Even") else:     print("Odd") # This code is contributed by Prerna saini

Output

Odd

Time Complexity: O(n)
Space Complexity: O(1)

Method: Using recursion

Python3

class Node:      def __init__(self, d):          self.data = d          self.next = None          self.head = None      # Function to check the length      # of linklist      def LinkedListLength(self, current=None):          # if current is None:              #current = self.head          if current is None:              return 0          return 1 + self.LinkedListLength(current.next)      # Push function      def push(self, info):          # Allocating node          node = Node(info)      # Next of new node to head          node.next = (self.head)      # head points to new node          (self.head) = node   # Driver code head = Node(0)   # Adding elements to Linked List  head.push(4)  head.push(5)  head.push(7)  head.push(2)  head.push(9)  head.push(6)  head.push(1)  head.push(2)  head.push(0)  head.push(5)   length = head.LinkedListLength()   # Checking for length of  # linklist  if length % 2 == 0:      print("Even")  else:      print("Odd")  # This code is contributed by Vinay Pinjala.

Output

Even

Time Complexity: O(n)
Auxiliary Space: O(n)

Please refer complete article on Check whether the length of given linked list is Even or Odd for more details!

Method: Using Two pointer approach:

Python3

# Define the Node class to create nodes for the linked list class Node:     def __init__(self, data):         self.data = data         self.next = None # Define the LinkedList class to create and manage linked lists class LinkedList:     def __init__(self):         self.head = None     # Function to determine the length of the linked list     def length(self):         slow_ptr = self.head # Initialize the slow pointer to the head of the list         fast_ptr = self.head # Initialize the fast pointer to the head of the list         # Move the slow pointer one step at a time         # Move the fast pointer two steps at a time         while fast_ptr is not None and fast_ptr.next is not None:             slow_ptr = slow_ptr.next             fast_ptr = fast_ptr.next.next         # If the fast pointer reaches the end of the list, the length is even         if fast_ptr is None:             return "Even"         # If the fast pointer reaches the last node of the list, the length is odd         else:             return "Odd" # Initialize a linked list and add some nodes to it linked_list = LinkedList() linked_list.head = Node(1) linked_list.head.next = Node(2) linked_list.head.next.next = Node(3) linked_list.head.next.next.next = Node(4) # Determine the length of the linked list length = linked_list.length() print("Length:", length) #This code is contributed by Jyothi pinjala.