C Exercises: Copy of a singly linked list with random pointers

Last update on August 02 2025 12:54:46 (UTC/GMT +8 hours)

18. Copy with Random Pointers Challenges

Write a C program to create a copy of a singly linked list with random pointers.

Sample Solution:

C Code:

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

// Define a structure for a Node in a singly linked list
struct Node {
    int data;
    struct Node *next, *random;
};

// Function to create a new node with given data
struct Node* newNode(int data) {
    // Allocate memory for a new node
    struct Node* node = (struct Node*) malloc(sizeof(struct Node));
    // Set the data for the new node
    node->data = data;
    // Set the next and random pointers of the new node to NULL
    node->next = NULL;
    node->random = NULL;
    return node;
}

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

// Function to perform deep copy of a linked list with random pointers
struct Node *copyList(struct Node *head) {
    struct Node *curr = head, *temp;

    // Insert a new node after each node in the original list
    while (curr) {
        temp = curr->next;
        curr->next = newNode(curr->data);
        curr->next->next = temp;
        curr = temp;
    }

    curr = head;

    // Copy the random pointers of the original list
    while (curr) {
        if (curr->random)
            curr->next->random = curr->random->next;
        curr = curr->next->next;
    }

    struct Node *original = head, *copy = head->next;

    // Split the original and copy lists
    temp = copy;
    while (original && copy) {
        original->next = original->next ? original->next->next : NULL;
        copy->next = copy->next ? copy->next->next : NULL;
        original = original->next;
        copy = copy->next;
    }

    return temp; // Return the head of the copied list
} 

// Function to print the elements and their corresponding random nodes in a linked list
void printList(struct Node *head) {
    while (head) {
        printf("Data: %d, Random: %d\n", head->data, head->random->data);
        head = head->next;
    }
}

// Main function where the execution starts
int main() {
    // Create a singly linked list with nodes and random pointers
    struct Node *head = newNode(1);
    head->next = newNode(2);
    head->next->next = newNode(3);
    head->next->next->next = newNode(5);
    head->next->next->next->next = newNode(7);

    // Set the random pointers for some nodes in the list
    head->random = head->next->next;
    head->next->random = head->next->next->next;
    head->next->next->random = head->next->next->next->next;
    head->next->next->next->random = head;
    head->next->next->next->next->random = head->next->next;

    // Copy the linked list with random pointers
    struct Node *copy = copyList(head);

    printf("Original singly list:\n");
    displayList(head); // Display the original list

    printf("\nAfter setting the random pointers:\n");
    printList(copy); // Display the copied list with random pointers

    return 0; // Indicates successful completion of the program
}

Sample Output:

Original singly list:
1 2 3 5 7 

After setting the random pointers:
Data: 1, Random: 3
Data: 2, Random: 5
Data: 3, Random: 7
Data: 5, Random: 1
Data: 7, Random: 3

Flowchart :

For more Practice: Solve these Related Problems:

Write a C program to create a deep copy of a singly linked list with random pointers using a hash map.
Write a C program to clone a linked list with random pointers by interweaving the original and copied nodes, then separating them.
Write a C program to copy a linked list with random pointers and then swap the random pointers between the original and the copy.
Write a C program to copy a linked list with random pointers and verify the integrity of the copied random links.

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