C Exercises: Interleave elements of two linked lists alternatively

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

// Structure defining a node in a singly linked list
struct Node {
    int data;           // Data stored in the node
    struct Node* next;  // Pointer to the next node
};

// Function to insert a new node at the end of a linked list
void append_data(struct Node** head, int data) {
    struct Node* new_node = (struct Node*) malloc(sizeof(struct Node)); // Allocate memory for a new node
    new_node->data = data; // Assign data to the new node
    new_node->next = NULL; // Initialize the next pointer as NULL

    // Check if the linked list is empty
    if (*head == NULL) {
        *head = new_node; // If empty, make the new node as the head
    } else {
        struct Node* last = *head;
        while (last->next != NULL) {
            last = last->next; // Traverse to the last node of the list
        }
        last->next = new_node; // Append the new node to the end of the list
    }
}

// Function to interleave elements of two linked lists alternatively
void interleave(struct Node** head1, struct Node** head2) {
    if (*head1 == NULL || *head2 == NULL) {
        return; // If either list is empty, return
    }

    struct Node* curr1 = *head1; // Pointer for the first list
    struct Node* curr2 = *head2; // Pointer for the second list

    // Loop to interleave the nodes of the two lists alternatively
    while (curr1 != NULL && curr2 != NULL) {
        struct Node* temp1 = curr1->next; // Store next nodes to maintain continuity
        struct Node* temp2 = curr2->next;

        curr1->next = curr2; // Interleave the nodes
        curr2->next = temp1;

        curr1 = temp1; // Move to the next nodes
        curr2 = temp2;
    }
}

// Function to print elements of a linked list
void printList(struct Node* node) {
    while (node != NULL) {
        printf("%d ", node->data); // Print the data of the current node
        node = node->next; // Move to the next node
    }
}

// Main function to demonstrate interleaving two linked lists alternatively
int main() {
    struct Node* head1 = NULL; // Initialize the first linked list
    struct Node* head2 = NULL; // Initialize the second linked list

    // Add nodes to the first linked list
    append_data(&head1, 1);
    append_data(&head1, 3);
    append_data(&head1, 5);
    append_data(&head1, 7);

    // Add nodes to the second linked list
    append_data(&head2, 2);
    append_data(&head2, 4);
    append_data(&head2, 6);
    append_data(&head2, 8);

    printf("Original Lists:\n");
    printf("List1: ");
    printList(head1); // Display the elements of the first list
    printf("\nList2: ");
    printList(head2); // Display the elements of the second list

    interleave(&head1, &head2); // Interleave the two lists alternatively

    printf("\n\nAfter interleaving the two linked lists alternatively:\n");
    printf("List1: ");
    printList(head1); // Display the modified first list after interleaving
    printf("\nList2: ");
    printList(head2); // Display the modified second list after interleaving

    return 0;
}