Remove all the Even Digit Sum Nodes from a Circular Singly Linked List

// C++ program to remove all
// the Even Digit Sum Nodes from a
// circular singly linked list

#include <bits/stdc++.h>
using namespace std;

// Structure for a node
struct Node {
    int data;
    struct Node* next;
};

// Function to insert a node at the beginning
// of a Circular linked list
void push(struct Node** head_ref, int data)
{
    // Create a new node and make head as next
    // of it.
    struct Node* ptr1
        = (struct Node*)malloc(
            sizeof(struct Node));

    struct Node* temp = *head_ref;
    ptr1->data = data;
    ptr1->next = *head_ref;

    // If linked list is not NULL then
    // set the next of last node
    if (*head_ref != NULL) {

        // Find the node before head
        // and update next of it.
        while (temp->next != *head_ref)
            temp = temp->next;

        temp->next = ptr1;
    }
    else

        // Point for the first node
        ptr1->next = ptr1;

    *head_ref = ptr1;
}

// Function to delete the node from a 
// Circular Linked list
void deleteNode(Node* head_ref, Node* del)
{
    struct Node* temp = head_ref;
    // Traverse list till not found
    // delete node
    while (temp->next != del) {
        temp = temp->next;
    }

    // Copy the address of the node
    temp->next = del->next;

    // Finally, free the memory
    // occupied by del
    free(del);

    return;
}

// Function to find the digit sum
// for a number
int digitSum(int num)
{
    int sum = 0;
    while (num) {
        sum += (num % 10);
        num /= 10;
    }

    return sum;
}

// Function to delete all the Even Digit Sum Nodes
// from the singly circular linked list
 Node* deleteEvenDigitSumNodes(Node* head)
{
    struct Node* ptr = head;

    struct Node* temp;

    //setting up the head node to the first non even digit sum node
    while(digitSum(ptr->data)%2==0){
        ptr=ptr->next;
        if(ptr==head){
            return NULL;
        }
    }
    temp = ptr;
    Node* temp2=ptr;
    ptr=ptr->next;
    //setting up the last node next to the first non even digit sum node
    while(ptr!=head){
            temp2=ptr;
        ptr=ptr->next;
    }
    temp2->next=temp;
    head=temp;
    ptr=head;
    // traverse list till the endl
    // if node is prime then delete it
    do {
            temp = ptr->next;
        // if node is prime
        if (digitSum(ptr->data)%2==0)
            deleteNode(head, ptr);
        ptr = temp;

    } while (ptr != head);
    return head;
}

// Function to print nodes in a
// given Circular linked list
void printList(struct Node* head)
{
      if(!head) printf("NULL");
    struct Node* temp = head;
    if (head != NULL) {
        do {
            printf("%d ", temp->data);
            temp = temp->next;
        } while (temp != head);
    }
}

// Driver code
int main()
{
    // Initialize lists as empty
    struct Node* head = NULL;

    // Created linked list will be
    // 9->11->34->6->13->21
    push(&head, 21);
    push(&head, 13);
    push(&head, 6);
    push(&head, 34);
    push(&head, 11);
    push(&head, 9);

    head = deleteEvenDigitSumNodes(head);

    printList(head);

    return 0;
}