C 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.

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 code
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");
    }
    else
    {
        printf("Odd");
    }
    return 0;
}

Output:

Odd

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

Using Recursion

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)
{
    if (head == NULL) return 0;
    return 1+LinkedListLength(head->next);
}

// 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 code
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");
    }
    else
    {
        printf("Odd");
    }
    return 0;
}

//This code is contributed Vinay Pinjala.

Output

Odd

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

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