Multiply two numbers represented by Linked Lists

Given two numbers represented by linked lists, write a function that returns the multiplication of these two linked lists.

Examples:

Input : 9->4->6
        8->4
Output : 79464

Input : 3->2->1
        1->2
Output : 3852

Solution: 
Traverse both lists and generate the required numbers to be multiplied and then return the multiplied values of the two numbers. 
Algorithm to generate the number from linked list representation: 

1) Initialize a variable to zero
2) Start traversing the linked list
3) Add the value of first node to this variable
4) From the second node, multiply the variable by 10
   and also take modulus of this value by 10^9+7
   and then add the value of the node to this 
   variable.
5) Repeat step 4 until we reach the last node of the list. 

Use the above algorithm with both of linked lists to generate the numbers. 

Below is the program for multiplying two numbers represented as linked lists:  

C++

// C++ program to Multiply two numbers
// represented as linked lists
#include<bits/stdc++.h>
#include<stdio.h>
using namespace std;

// Linked list node
struct Node
{
    int data;
    struct Node* next;
};

// Function to create a new node
// with given data
struct Node *newNode(int data)
{
    struct Node *new_node = (struct Node *) malloc(sizeof(struct Node));
    new_node->data = data;
    new_node->next = NULL;
    return new_node;
}

// Function to insert a node at the
// beginning of the Linked List
void push(struct Node** head_ref, int new_data)
{
    // allocate node
    struct Node* new_node = newNode(new_data);

    // link the old list of the new node
    new_node->next = (*head_ref);

    // move the head to point to the new node
    (*head_ref) = new_node;
}

// Multiply contents of two linked lists
long long multiplyTwoLists (Node* first, Node* second)
{
    long long N= 1000000007;
    long long num1 = 0, num2 = 0;
    while (first || second){

        if(first){
            num1 = ((num1)*10)%N + first->data;
            first = first->next;
        }

        if(second)
        {
            num2 = ((num2)*10)%N + second->data;
            second = second->next;
        }

    }
    return ((num1%N)*(num2%N))%N;
}

// A utility function to print a linked list
void printList(struct Node *node)
{
    while(node != NULL)
    {
        cout<<node->data;
        if(node->next)
            cout<<"->";
        node = node->next;
    }
    cout<<"\n";
}

// Driver program to test above function
int main()
{
    struct Node* first = NULL;
    struct Node* second = NULL;

    // create first list 9->4->6
    push(&first, 6);
    push(&first, 4);
    push(&first, 9);
    printf("First List is: ");
    printList(first);

    // create second list 8->4
    push(&second, 4);
    push(&second, 8);
    printf("Second List is: ");
    printList(second);

    // Multiply the two lists and see result
    cout<<"Result is: ";
    cout<<multiplyTwoLists(first, second);

    return 0;
}

// This code is contributed by Sania Kumari Gupta (kriSania804)

C

// C program to Multiply two numbers
// represented as linked lists
#include <stdio.h>
#include <stdlib.h>
// Linked list node
typedef struct Node {
    int data;
    struct Node* next;
} Node;

// Function to create a new node
// with given data
struct Node* newNode(int data)
{
    Node* new_node = (Node*)malloc(sizeof(Node));
    new_node->data = data;
    new_node->next = NULL;
    return new_node;
}

// Function to insert a node at the
// beginning of the Linked List
void push(struct Node** head_ref, int new_data)
{
    // allocate node
    struct Node* new_node = newNode(new_data);

    // link the old list of the new node
    new_node->next = (*head_ref);

    // move the head to point to the new node
    (*head_ref) = new_node;
}

// Multiply contents of two linked lists
long long multiplyTwoLists(Node* first, Node* second)
{
    long long N = 1000000007;
    long long num1 = 0, num2 = 0;
    while (first || second) {

        if (first) {
            num1 = ((num1)*10) % N + first->data;
            first = first->next;
        }

        if (second) {
            num2 = ((num2)*10) % N + second->data;
            second = second->next;
        }
    }
    return ((num1 % N) * (num2 % N)) % N;
}

// A utility function to print a linked list
void printList(struct Node* node)
{
    while (node != NULL) {
        printf("%d", node->data);
        if (node->next)
            printf("->");
        node = node->next;
    }
    printf("\n");
}

// Driver program to test above function
int main()
{
    struct Node* first = NULL;
    struct Node* second = NULL;

    // create first list 9->4->6
    push(&first, 6);
    push(&first, 4);
    push(&first, 9);
    printf("First List is: ");
    printList(first);

    // create second list 8->4
    push(&second, 4);
    push(&second, 8);
    printf("Second List is: ");
    printList(second);

    // Multiply the two lists and see result
    printf("Result is: ");
    printf("%lld", multiplyTwoLists(first, second));

    return 0;
}

// This code is contributed by Sania Kumari Gupta
// (kriSania804)

Java

// Java program to Multiply two numbers
// represented as linked lists
import java.util.*;

public class GFG{

    // Linked list node
    static class Node
    {
        int data;
        Node next;

        Node(int data){
            this.data = data;
            next = null;
        }
    }

    // Multiply contents of two linked lists
    static long multiplyTwoLists(Node first, Node second)
    {
        long N = 1000000007;
        long num1 = 0, num2 = 0;

        while (first != null || second !=  null){

            if(first != null){
                num1 = ((num1)*10)%N + first.data;
                first = first.next;
            }

            if(second != null)
            {
                num2 = ((num2)*10)%N + second.data;
                second = second.next;
            }

        }
        return ((num1%N)*(num2%N))%N;
    }

    // A utility function to print a linked list
    static void printList(Node node)
    {
        while(node != null)
        {
            System.out.print(node.data);
            if(node.next != null)
                System.out.print("->");
            node = node.next;
        }
        System.out.println();
    }

    // Driver program to test above function
    public static void main(String args[])
    {
        // create first list 9->4->6
        Node first = new Node(9);
        first.next = new Node(4);
        first.next.next = new Node(6);
        System.out.print("First List is: ");
        printList(first);

        // create second list 8->4
        Node second = new Node(8);
        second.next = new Node(4);
        System.out.print("Second List is: ");
        printList(second);

        // Multiply the two lists and see result
        System.out.print("Result is: ");
        System.out.println(multiplyTwoLists(first, second));
    }
}

// This code is contributed by adityapande88

Python3

# Python3 to multiply two numbers
# represented as Linked Lists

# Linked list node class
class Node:

    # Function to initialize the node
    def __init__(self, data):

        self.data = data
        self.next = None

# Linked List Class
class LinkedList:

    # Function to initialize the
    # LinkedList class.
    def __init__(self):

        # Initialize head as None
        self.head = None

    # Function to insert a node at the
    # beginning of the Linked List
    def push(self, new_data):

        # Create a new Node
        new_node = Node(new_data)

        # Make next of the new Node as head
        new_node.next = self.head

        # Move the head to point to new Node
        self.head = new_node

    # Function to print the Linked List
    def printList(self):

        ptr = self.head

        while (ptr != None):
            print(ptr.data, end = '')
            if ptr.next != None:
                print('->', end = '')

            ptr = ptr.next

        print()

# Multiply contents of two Linked Lists
def multiplyTwoLists(first, second):

    num1 = 0
    num2 = 0

    first_ptr = first.head
    second_ptr = second.head

    while first_ptr != None or second_ptr != None:
        if first_ptr != None:
            num1 = (num1 * 10) + first_ptr.data
            first_ptr = first_ptr.next

        if second_ptr != None:
            num2 = (num2 * 10) + second_ptr.data
            second_ptr = second_ptr.next

    return num1 * num2

# Driver code
if __name__=='__main__':

    first = LinkedList()
    second = LinkedList()

    # Create first Linked List 9->4->6
    first.push(6)
    first.push(4)
    first.push(9)

    # Printing first Linked List
    print("First list is: ", end = '')
    first.printList()

    # Create second Linked List 8->4
    second.push(4)
    second.push(8)

    # Printing second Linked List
    print("Second List is: ", end = '')
    second.printList()

    # Multiply two linked list and
    # print the result
    result = multiplyTwoLists(first, second)
    print("Result is: ", result)

# This code is contributed by kirtishsurangalikar

C#

// C++ program to Multiply two numbers
// represented as linked lists
using System;
public class GFG
{

    // Linked list node
    public class Node {
        public int data;
        public Node next;
        public Node(int data)
        {
            this.data = data;
            this.next = null;
        }
    }
    // Multiply contents of two linked lists
    public static long multiplyTwoLists(Node first,
                                        Node second)
    {
        var N = 1000000007;
        var num1 = 0;
        var num2 = 0;
        while (first != null || second != null) {
            if (first != null) {
                num1 = ((num1)*10) % N + first.data;
                first = first.next;
            }
            if (second != null) {
                num2 = ((num2)*10) % N + second.data;
                second = second.next;
            }
        }
        return ((num1 % N) * (num2 % N)) % N;
    }
    // A utility function to print a linked list
    public static void printList(Node node)
    {
        while (node != null) {
            Console.Write(node.data);
            if (node.next != null) {
                Console.Write("->");
            }
            node = node.next;
        }
        Console.WriteLine();
    }
    // Driver program to test above function
    public static void Main(String[] args)
    {
        // create first list 9->4->6
        var first = new Node(9);
        first.next = new Node(4);
        first.next.next = new Node(6);
        Console.Write("First List is: ");
        GFG.printList(first);

        // create second list 8->4
        var second = new Node(8);
        second.next = new Node(4);
        Console.Write("Second List is: ");
        GFG.printList(second);

        // Multiply the two lists and see result
        Console.Write("Result is: ");
        Console.WriteLine(
            GFG.multiplyTwoLists(first, second));
    }
}

// This code is contributed by mukulsomukesh

Javascript

<script>
// Javascript program to Multiply two numbers
// represented as linked lists

// Linked list node
class Node
{
    constructor(data)
    {
        this.data=data;
        this.next = null;
    }
}

// Multiply contents of two linked lists
function multiplyTwoLists(first,second)
{
     let N = 1000000007;
        let num1 = 0, num2 = 0;

        while (first != null || second !=  null){

            if(first != null){
                num1 = ((num1)*10)%N + first.data;
                first = first.next;
            }

            if(second != null)
            {
                num2 = ((num2)*10)%N + second.data;
                second = second.next;
            }

        }
        return ((num1%N)*(num2%N))%N;
    }




// A utility function to print a linked list
    function printList(node)
    {
        while(node != null)
        {
            document.write(node.data);
            if(node.next != null)
                document.write("->");
            node = node.next;
        }
        document.write("<br>");
    }

// Driver program to test above function
// create first list 9->4->6
let first = new Node(9);
first.next = new Node(4);
first.next.next = new Node(6);
document.write("First List is: ");
printList(first);

// create second list 8->4
let second = new Node(8);
second.next = new Node(4);
document.write("Second List is: ");
printList(second);

// Multiply the two lists and see result
document.write("Result is: ");
document.write(multiplyTwoLists(first, second)+"<br>");

// This code is contributed by avanitrachhadiya2155
</script>

Output

First List is: 9->4->6
Second List is: 8->4
Result is: 79464

Time Complexity: O(max(n1, n2)), where n1 and n2 represents the number of nodes present in the first and second linked list respectively.
Auxiliary Space: O(1), no extra space is required, so it is a constant.

Asked in: Amazon

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