Question

Write C language code for a function that takes a doubly linked list as a parameter and deletes all the nodes in even positions from the first to the last after displaying the content of each node to the console.

Answer 1

function to delete all nodes at even position in C

// function to delete a node in a Doubly Linked List. 
// head_ref --> pointer to head node pointer. 
// del --> pointer to node to be deleted 
void deleteNode(Node** head_ref, Node* del) 
{ 
        // base case 
        if (*head_ref == NULL || del == NULL) 
                return; 

        // If node to be deleted is head node 
        if (*head_ref == del) 
                *head_ref = del->next; 

        // Change next only if node to be 
        // deleted is NOT the last node 
        if (del->next != NULL) 
                del->next->prev = del->prev; 

        // Change prev only if node to be 
        // deleted is NOT the first node 
        if (del->prev != NULL) 
                del->prev->next = del->next; 

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

        return; 
} 

// function to delete all the nodes at even position
// from the doubly linked list 
void deleteEvenPositionNodes(Node** head_ref) 
{ 
    int i = 0;
        Node* ptr = *head_ref; 
        Node* next; 

        while (ptr != NULL) { 
            i++;
                next = ptr->next; 
                printf("%d\n", ptr->data);
                if (i % 2 == 0) 
                        deleteNode(head_ref, ptr); 
                ptr = next; 
        } 
}