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

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)

## 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.`

Output
`Length: Even`

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

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