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Check whether the length of given linked list is Even or Odd

  • Difficulty Level : Basic
  • Last Updated : 13 May, 2021

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.

 

C++




// C++ program to check length
// of a given linklist
#include <bits/stdc++.h>
using namespace std;
 
// Defining structure
class Node
{
    public:
    int data;
    Node* next;
};
 
// Function to check the length of linklist
int LinkedListLength(Node* head)
{
    while (head && head->next)
    {
        head = head->next->next;
    }
    if (!head)
        return 0;
    return 1;
}
     
// Push function
void push(Node** head, int info)
{
    // Allocating node
    Node* node = new Node();
     
    // Info into node
    node->data = info;
     
    // Next of new node to head
    node->next = (*head);
 
    // head points to new node
    (*head) = node;
}
 
// Driver code
int main(void)
{
    Node* head = NULL;
     
    // Adding elements to Linked List
    push(&head, 4);
    push(&head, 5);
    push(&head, 7);
    push(&head, 2);
    push(&head, 9);
    push(&head, 6);
    push(&head, 1);
    push(&head, 2);
    push(&head, 0);
    push(&head, 5);
    push(&head, 5);
    int check = LinkedListLength(head);
     
    // Checking for length of
    // linklist
    if(check == 0)
    {
        cout << "Even\n";
    }
    else
    {
        cout << "Odd\n";
    }
    return 0;
}
 
// This is code is contributed by rathbhupendra

C




// C program to check length
// of a given linklist
#include<stdio.h>
#include<stdlib.h>
 
// Defining structure
struct Node
{
    int data;
    struct Node* next;
};
 
// Function to check the length of linklist
int LinkedListLength(struct Node* head)
{
    while (head && head->next)
    {
        head = head->next->next;
    }
    if (!head)
        return 0;
    return 1;
}
     
// Push function
void push(struct Node** head, int info)
{
    // Allocating node
    struct Node* node = (struct Node*) malloc(sizeof(struct Node));
     
    // Info into node
    node->data = info;
     
    // Next of new node to head
    node->next = (*head);
 
    // head points to new node
    (*head) = node;
}
 
// Driver function
int main(void)
{
    struct Node* head = NULL;
     
    // Adding elements to Linked List
    push(&head, 4);
    push(&head, 5);
    push(&head, 7);
    push(&head, 2);
    push(&head, 9);
    push(&head, 6);
    push(&head, 1);
    push(&head, 2);
    push(&head, 0);
    push(&head, 5);
    push(&head, 5);
    int check = LinkedListLength(head);
     
    // Checking for length of
    // linklist
    if(check == 0)
    {
        printf("Even\n");
    }
    else
    {
        printf("Odd\n");
    }
    return 0;
}

Java




/*package whatever //do not write package name here */
 
import java.io.*;
 
// Java program to check length
// of a given linklist
class GfG
{
 
// Defining structure
static class Node
{
    int data;
    Node next;
}
 
// Function to check the length of linklist
static int LinkedListLength(Node head)
{
    while (head != null && head.next != null)
    {
        head = head.next.next;
    }
    if (head == null)
        return 0;
    return 1;
}
     
// Push function
static void push(Node head, int info)
{
    // Allocating node
    Node node = new Node();
     
    // Info into node
    node.data = info;
     
    // Next of new node to head
    node.next = (head);
 
    // head points to new node
    (head) = node;
}
 
// Driver code
public static void main(String[] args)
{
    Node head = null;
     
    // Adding elements to Linked List
    push(head, 4);
    push(head, 5);
    push(head, 7);
    push(head, 2);
    push(head, 9);
    push(head, 6);
    push(head, 1);
    push(head, 2);
    push(head, 0);
    push(head, 5);
    push(head, 5);
    int check = LinkedListLength(head);
     
    // Checking for length of
    // linklist
    if(check == 0)
    {
        System.out.println("Odd");
    }
    else
    {
        System.out.println("Even");
    }
}
}
 
// This code is contributed by Prerna saini

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

C#




// C# program to check length
// of a given linklist
using System;
 
class GfG
{
 
// Defining structure
class Node
{
    public int data;
    public Node next;
}
 
// Function to check the length of linklist
static int LinkedListLength(Node head)
{
    while (head != null && head.next != null)
    {
        head = head.next.next;
    }
    if (head == null)
        return 0;
    return 1;
}
     
// Push function
static void push(Node head, int info)
{
    // Allocating node
    Node node = new Node();
     
    // Info into node
    node.data = info;
     
    // Next of new node to head
    node.next = (head);
 
    // head points to new node
    (head) = node;
}
 
// Driver code
public static void Main()
{
    Node head = null;
     
    // Adding elements to Linked List
    push(head, 4);
    push(head, 5);
    push(head, 7);
    push(head, 2);
    push(head, 9);
    push(head, 6);
    push(head, 1);
    push(head, 2);
    push(head, 0);
    push(head, 5);
    push(head, 5);
    int check = LinkedListLength(head);
     
    // Checking for length of
    // linklist
    if(check == 0)
    {
        Console.WriteLine("Odd");
    }
    else
    {
        Console.WriteLine("Even");
    }
}
}
 
// This code has been contributed
// by PrinciRaj1992

Javascript




<script>
 
// JavaScript program to check length
// of a given linklist
 
 
    // Defining structure
     class Node {
            constructor() {
                this.data = 0;
                this.next = null;
            }
        }
    // Function to check the length of linklist
    function LinkedListLength( head) {
        while (head != null && head.next != null) {
            head = head.next.next;
        }
        if (head == null)
            return 0;
        return 1;
    }
 
    // Push function
    function push( head , info) {
        // Allocating node
         node = new Node();
 
        // Info into node
        node.data = info;
 
        // Next of new node to head
        node.next = (head);
 
        // head points to new node
        (head) = node;
    }
 
    // Driver code
     
         head = null;
 
        // Adding elements to Linked List
        push(head, 4);
        push(head, 5);
        push(head, 7);
        push(head, 2);
        push(head, 9);
        push(head, 6);
        push(head, 1);
        push(head, 2);
        push(head, 0);
        push(head, 5);
        push(head, 5);
        var check = LinkedListLength(head);
 
        // Checking for length of
        // linklist
        if (check == 0) {
            document.write("Odd");
        } else {
            document.write("Even");
        }
 
// This code contributed by umadevi9616
 
</script>

Output:  

Odd

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

This article is contributed by Sahil Rajput. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
 


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