Find the product of first k nodes of the given Linked List

Given a pointer to the head of a singly linked list and an integer k. The task is to find the product of the first k nodes of the linked list.

Examples:

Input: 10 -> 6 -> 8 -> 4 -> 12, k = 2 
Output: 60 
10 * 6 = 60

Input: 15 -> 7 -> 9 -> 5 -> 16 -> 14, k = 4 
Output: 4725 
15 * 7 * 9 * 5 = 4725 

Approach: Set prod = 1 (required product) and count = 0 (count of nodes traversed). Now, start traversing the nodes of the linked list from left to right and update count = count + 1 and prod = prod * currNode -> data with every traversed node while count < k. Print the value of the prod in the end.

Below is the implementation of the above approach: 

C++

// C++ program to find the product of first
// 'k' nodes of the Linked List
#include <bits/stdc++.h>
using namespace std;
#define ll long long int

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

// 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 = new Node;

    /* put in the data */
    new_node->data = new_data;

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

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

// Function to return the product of
// first k nodes of the given linked list
ll product(struct Node* head, int k)
{
    if (k <= 0)
        return 0;

    ll prod = 1;
    int i = 0;
    Node* node = head;

    // Traverse the list from left to right
    while (i < k) {

        // Update product
        prod = prod * node->data;

        // Move to the next node
        node = node->next;
        i++;
    }

    // Return the required product
    return prod;
}

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

    // Linked list 10 -> 6 -> 8 -> 4 -> 12
    push(&head, 12);
    push(&head, 4);
    push(&head, 8);
    push(&head, 6);
    push(&head, 10);

    int k = 2;
    cout << product(head, k);
    return 0;
}

Java

// Java program to find the product of first
// 'k' nodes of the Linked List
class Solution
{

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

// Function to insert a node at the
// beginning of the linked list
static Node push( Node head_ref, int new_data)
{
    /* allocate node */
    Node new_node = new Node();

    /* put in the data */
    new_node.data = new_data;

    /* link the old list to the new node */
    new_node.next = (head_ref);

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

    return head_ref;
}

// Function to return the product of
// first k nodes of the given linked list
static long product( Node head, int k)
{
    if (k <= 0)
        return 0;

    long prod = 1;
    int i = 0;
    Node node = head;

    // Traverse the list from left to right
    while (i < k)
    {

        // Update product
        prod = prod * node.data;

        // Move to the next node
        node = node.next;
        i++;
    }

    // Return the required product
    return prod;
}

// Driver code
public static void main(String args[])
{
    Node head = new Node();

    // Linked list 10 . 6 . 8 . 4 . 12
    head=push(head, 12);
    head=push(head, 4);
    head=push(head, 8);
    head=push(head, 6);
    head=push(head, 10);

    int k = 2;
    System.out.println( product(head, k));

}
}

// This code is contributed by Arnab Kundu

Python3

# Python3 program to find the product
# of first 'k' nodes of the Linked List
import math

#define ll long long

# A Linked list node
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

# Function to insert a node at the
# beginning of the linked list
def push(head_ref, new_data):

    # allocate node
    new_node = Node(new_data)

    # put in the data
    new_node.data = new_data

    # link the old list to the new node
    new_node.next = head_ref

    # move the head to po to the new node
    head_ref = new_node
    return head_ref

# Function to return the product of
# first k nodes of the given linked list
def product(head, k):
    if (k <= 0):
        return 0

    prod = 1
    i = 0
    node = head

    # Traverse the list from left to right
    while (i < k):

        # Update product
        prod = prod * node.data

        # Move to the next node
        node = node.next
        i = i + 1

    # Return the required product
    return prod

# Driver code
if __name__=='__main__':
    head = None

    # Linked list 10 . 6 . 8 . 4 . 12
    head = push(head, 12);
    head = push(head, 4);
    head = push(head, 8);
    head = push(head, 6);
    head = push(head, 10);

    k = 2
    print(product(head, k))

# This code is contributed by Srathore

C#

// C# program to find the product of first
// 'k' nodes of the Linked List
using System;

class GFG
{

/* A Linked list node */
class Node
{
    public int data;
    public Node next;
}

// Function to insert a node at the
// beginning of the linked list
static Node push( Node head_ref, int new_data)
{
    /* allocate node */
    Node new_node = new Node();

    /* put in the data */
    new_node.data = new_data;

    /* link the old list to the new node */
    new_node.next = (head_ref);

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

    return head_ref;
}

// Function to return the product of
// first k nodes of the given linked list
static long product( Node head, int k)
{
    if (k <= 0)
        return 0;

    long prod = 1;
    int i = 0;
    Node node = head;

    // Traverse the list from left to right
    while (i < k)
    {

        // Update product
        prod = prod * node.data;

        // Move to the next node
        node = node.next;
        i++;
    }

    // Return the required product
    return prod;
}

// Driver code
public static void Main()
{
    Node head = new Node();

    // Linked list 10 . 6 . 8 . 4 . 12
    head=push(head, 12);
    head=push(head, 4);
    head=push(head, 8);
    head=push(head, 6);
    head=push(head, 10);

    int k = 2;
    Console.WriteLine( product(head, k));
}
}

// This code is contributed by PrinciRaj1992

Javascript

<script>
// javascript program to find the product of first
// 'k' nodes of the Linked List

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

    // Function to insert a node at the
    // beginning of the linked list
    function push(head_ref , new_data) {
        /* allocate node */
        var new_node = new Node();

        /* put in the data */
        new_node.data = new_data;

        /* link the old list to the new node */
        new_node.next = (head_ref);

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

        return head_ref;
    }

    // Function to return the product of
    // first k nodes of the given linked list
    function product(head , k) {
        if (k <= 0)
            return 0;

        var prod = 1;
        var i = 0;
        var node = head;

        // Traverse the list from left to right
        while (i < k) {

            // Update product
            prod = prod * node.data;

            // Move to the next node
            node = node.next;
            i++;
        }

        // Return the required product
        return prod;
    }

    // Driver code

        var head = new Node();

        // Linked list 10 . 6 . 8 . 4 . 12
        head = push(head, 12);
        head = push(head, 4);
        head = push(head, 8);
        head = push(head, 6);
        head = push(head, 10);

        var k = 2;
        document.write(product(head, k));


// This code contributed by Rajput-Ji
</script>

Output:

60