C Exercises: Merge alternate nodes of two linked lists

Last update on August 04 2025 13:01:33 (UTC/GMT +8 hours)

34. Alternate Node Merging Challenges

Write a C program to to merge alternate nodes of two singly linked lists.

Sample Solution:

C Code:

#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 push a new node to the front of the linked list
void push_node(struct Node** head_ref, int new_data) {
    struct Node* new_node = (struct Node*)malloc(sizeof(struct Node));  // Allocate memory for a new node
    new_node->data = new_data;  // Assign data to the new node
    new_node->next = (*head_ref);  // Make the new node point to the current head
    (*head_ref) = new_node;  // Update the head to point to the new node
}

// Function to merge alternate nodes of two linked lists
void merge_alternate_Nodes(struct Node** head1_ref, struct Node** head2_ref) {
    struct Node* p1 = *head1_ref;  // Pointer for the first list
    struct Node* p2 = *head2_ref;  // Pointer for the second list

    while (p1 != NULL && p2 != NULL) {
        struct Node* temp = p1->next;  // Store the next node of the first list
        p1->next = p2;  // Make the current node of the first list point to the current node of the second list
        p2 = p2->next;  // Move to the next node in the second list
        p1->next->next = temp;  // Make the node from the second list point to the next node of the first list
        p1 = temp;  // Move to the next node in the first list
    }

    *head2_ref = p2;  // Update the second list's head to the remaining nodes
}

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

// Main function to demonstrate merging alternate nodes of two linked lists
int main() {
    struct Node* head1 = NULL;  // Initialize the first linked list as empty
    struct Node* head2 = NULL;  // Initialize the second linked list as empty

    // Push elements to the first linked list
    push_node(&head1, 1);
    push_node(&head1, 3);
    push_node(&head1, 5);
    push_node(&head1, 7);
    push_node(&head1, 9);

    // Push elements to the second linked list
    push_node(&head2, 2);
    push_node(&head2, 4);
    push_node(&head2, 6);
    push_node(&head2, 8);
    push_node(&head2, 10);

    printf("First linked list: ");
    displayList(head1);  // Display the first linked list

    printf("Second linked list: ");
    displayList(head2);  // Display the second linked list

    merge_alternate_Nodes(&head1, &head2);  // Merge alternate nodes of both lists

    printf("Merged linked list: ");
    displayList(head1);  // Display the merged linked list

    return 0;
}

Sample Output:

First linked list: 9 7 5 3 1 
Second linked list: 10 8 6 4 2 
Merged linked list: 9 10 7 8 5 6 3 4 1 2

Flowchart :

For more Practice: Solve these Related Problems:

Write a C program to merge alternate nodes from two linked lists after reversing the second list.
Write a C program to merge alternate nodes from two lists, handling cases where the lists are of unequal lengths by appending extra nodes at the end.
Write a C program to recursively merge alternate nodes from two singly linked lists without using extra memory.
Write a C program to merge alternate nodes from two linked lists and then swap values for nodes that are out of sorted order.

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