1.#include <stdio.h>
#include <stdlib.h>
 

struct Node {
    int data;
    struct Node* next;
};
 

void insertAfter(struct Node* prev_node, int new_data)
{
    
    if (prev_node == NULL) {
        printf("The given previous node cannot be NULL");
        return;
    }
 

    struct Node* new_node
        = (struct Node*)malloc(sizeof(struct Node));
 
    
    new_node->data = new_data;
 
    
    new_node->next = prev_node->next;
 
   
    prev_node->next = new_node;
}
 

void push(struct Node** head_ref, int new_data)
{
    struct Node* new_node
        = (struct Node*)malloc(sizeof(struct Node));
    new_node->data = new_data;
    new_node->next = (*head_ref);
    (*head_ref) = new_node;
}
 

void printList(struct Node* node)
{
    while (node != NULL) {
        printf(" %d", node->data);
        node = node->next;
    }
    printf("\n");
}
 

int main()
{

    struct Node* head = NULL;
 
    push(&head, 6);
    push(&head, 5);
    push(&head, 4);
    push(&head, 3);
    push(&head, 2);
 
    printf("Created Linked list is: ");
    printList(head);
 
    
    insertAfter(head, 1);
 
    printf("After inserting 1 after 2: ");
    printList(head);
 
    return 0;
}

2.#include <stdio.h>
#include <stdlib.h>

struct Node {
    int data;
    struct Node* next;
};


void insertAtHead(struct Node** head, int newData) {
    
    struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
    if (newNode == NULL) {
        fprintf(stderr, "Memory allocation failed.\n");
        exit(1); // Exit the program if memory allocation fails
    }
    
    newNode->data = newData;

    
    newNode->next = *head;

    
    *head = newNode;
}

int main() {
    
    struct Node* head = NULL;

    
    insertAtHead(&head, 3);
    insertAtHead(&head, 2);
    insertAtHead(&head, 1);

   

    
    struct Node* current = head;
    while (current != NULL) {
        printf("%d -> ", current->data);
        current = current->next;
    }
    printf("NULL\n");

    return 0;
}