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

Last Updated : 19 Jan, 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.

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"; 
    } 
    else
    { 
        cout << "Odd"; 
    } 
    return 0; 
} 
// This is code is contributed by rathbhupendra

Output:

Odd

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

Method: Using Recursion

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; 
}; 
 
//Recursive Function to check the length 
// of linklist 
int LinkedListLength(Node* head) 
{ 
    if(head == NULL) 
    {
        return 0;
    }
    return 1 + LinkedListLength(head->next); 
}
 
     
// 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"; 
    } 
    else
    { 
        cout << "Odd"; 
    } 
    return 0; 
} 
// This is code is contributed by vinay pinjala.