Product of the alternate nodes of linked list

Given a linked list, the task is to print the product of alternate nodes of the given linked list.

Examples: 

Input : 1 -> 8 -> 3 -> 10 -> 17 -> 22 -> 29 -> 42
Output : 1479
Alternate nodes : 1 -> 3 -> 17 -> 29

Input : 10 -> 17 -> 33 -> 38 -> 73
Output : 24090 
Alternate nodes : 10 -> 33 -> 73 

Iterative Approach:

1. Traverse the whole linked list.
2. Set prod = 1 and count=0.
3. Multiply the data of the node with the prod when the count is even.
4. Visit the next node.

Below is the implementation of this approach:

C++

// C++ code to print the product of Alternate Nodes
#include <bits/stdc++.h>
using namespace std;

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

/* Function to get the product of alternate
nodes of the linked list */
int productAlternateNode(struct Node* head)
{
    int count = 0;
    int prod = 1;

    while (head != NULL) {

        // when count is even product the data of node
        if (count % 2 == 0)
            prod *= head->data;

        // count the nodes
        count++;

        // move on the next node.
        head = head->next;
    }
    return prod;
}

// Function to push node at head
void push(struct Node** head_ref, int new_data)
{
    struct Node* new_node = new  Node;
    new_node->data = new_data;
    new_node->next = (*head_ref);
    (*head_ref) = new_node;
}

// Driver code
int main()
{
    /* Start with the empty list */
    struct Node* head = NULL;

    /* Use push() function to construct
    the below list 8 -> 23 -> 11 -> 29 -> 12 */
    push(&head, 12);
    push(&head, 29);
    push(&head, 11);
    push(&head, 23);
    push(&head, 8);

    cout << productAlternateNode(head);

    return 0;
}

// This code is contributed by shivani singh

C

// C code to print the product of Alternate Nodes
#include <stdio.h>
#include <stdlib.h>

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

/* Function to get the product of alternate
   nodes of the linked list */
int productAlternateNode(struct Node* head)
{
    int count = 0;
    int prod = 1;

    while (head != NULL) {

        // when count is even product the data of node
        if (count % 2 == 0)
            prod *= head->data;

        // count the nodes
        count++;

        // move on the next node.
        head = head->next;
    }
    return prod;
}

// Function to push node at head
void push(struct Node** head_ref, int new_data)
{
    struct Node* new_node = (struct Node*)malloc(sizeof(struct Node));
    new_node->data = new_data;
    new_node->next = (*head_ref);
    (*head_ref) = new_node;
}

// Driver code
int main()
{
    /* Start with the empty list */
    struct Node* head = NULL;

    /* Use push() function to construct
       the below list 8 -> 23 -> 11 -> 29 -> 12 */
    push(&head, 12);
    push(&head, 29);
    push(&head, 11);
    push(&head, 23);
    push(&head, 8);

    printf(" %d ", productAlternateNode(head));

    return 0;
}

Java

// Java code to print the product of Alternate Nodes
class GFG
{

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

/* Function to get the alternate
nodes of the linked list */
static int productAlternateNode( Node head)
{
    int count = 0;
    int product = 1;

    while (head != null)
    {

        // when count is even product the nodes
        if (count % 2 == 0)
            product *= head.data;

        // count the nodes
        count++;

        // move on the next node.
        head = head.next;
    }
    return product;
}

// Function to push node at head
static Node push( Node head_ref, int new_data)
{
    Node new_node =new Node();
    new_node.data = new_data;
    new_node.next = (head_ref);
    (head_ref) = new_node;
    return head_ref;
}

// Driver code
public static void main(String args[])
{
    /* Start with the empty list */
    Node head = null;

    /* Use push() function to con
    the below list 8 . 23 . 11 . 29 . 12 */
    head = push(head, 12);
    head = push(head, 29);
    head = push(head, 11);
    head = push(head, 23);
    head = push(head, 8);

    System.out.printf(" %d ", productAlternateNode(head));
}
}


// This code is contributed by Arnab Kundu

Python3

# Python3 code to print the
# product of Alternate Nodes
import math

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

# Function to get the product of alternate
# nodes of the linked list
def productAlternateNode(head):
    count = 0
    prod = 1

    while (head != None):

        # when count is even, product
        # the data of node
        if (count % 2 == 0):
            prod *= head.data

        # count the nodes
        count = count + 1

        # move on the next node.
        head = head.next

    return prod

# Function to head=push node at head
def push(head_ref, new_data):
    new_node = Node(new_data)

    #new_node.data = new_data
    new_node.next = head_ref
    head_ref = new_node
    return head_ref

# Driver code
if __name__=='__main__':

    # Start with the empty list
    head = None

    # Use head=push() function to construct
    #the below list 8 . 23 . 11 . 29 . 12
    head = push(head, 12)
    head = push(head, 29)
    head = push(head, 11)
    head = push(head, 23)
    head = push(head, 8)

    print(productAlternateNode(head))

# This code is contributed by Srathore

C#

// C# code to print the product of Alternate Nodes
using System;

class GFG
{

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

/* Function to get the alternate
nodes of the linked list */
static int productAlternateNode( Node head)
{
    int count = 0;
    int product = 1;

    while (head != null)
    {

        // when count is even product the nodes
        if (count % 2 == 0)
            product *= head.data;

        // count the nodes
        count++;

        // move on the next node.
        head = head.next;
    }
    return product;
}

// Function to push node at head
static Node push( Node head_ref, int new_data)
{
    Node new_node =new Node();
    new_node.data = new_data;
    new_node.next = (head_ref);
    (head_ref) = new_node;
    return head_ref;
}

// Driver code
public static void Main(String []args)
{
    /* Start with the empty list */
    Node head = null;

    /* Use push() function to con
    the below list 8 . 23 . 11 . 29 . 12 */
    head = push(head, 12);
    head = push(head, 29);
    head = push(head, 11);
    head = push(head, 23);
    head = push(head, 8);

    Console.Write(" {0} ", productAlternateNode(head));
}
}

// This code has been contributed by 29AjayKumar

Javascript

<script>
    // javascript code to print the product of Alternate Nodes     /* Link list node */
    class Node {
        constructor(val) {
            this.data = val;
            this.next = null;
        }
    }
    /*
     * Function to get the alternate nodes of the linked list
     */
    function productAlternateNode(head) {
        var count = 0;
        var product = 1;

        while (head != null) {

            // when count is even product the nodes
            if (count % 2 == 0)
                product *= head.data;

            // count the nodes
            count++;

            // move on the next node.
            head = head.next;
        }
        return product;
    }

    // Function to push node at head
    function push(head_ref , new_data) {
        var new_node = new Node();
        new_node.data = new_data;
        new_node.next = (head_ref);
        (head_ref) = new_node;
        return head_ref;
    }

    // Driver code

        /* Start with the empty list */
        var head = null;

        /*
         * Use push() function to construct  the below list 8 . 23 . 11 . 29 . 12
         */
        head = push(head, 12);
        head = push(head, 29);
        head = push(head, 11);
        head = push(head, 23);
        head = push(head, 8);

        document.write( productAlternateNode(head));

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

Output

1056

Complexity Analysis:

• Time Complexity: O(N)
• Auxiliary Space: O(1)

Recursive Approach: 

1. Initialize a static variable(say flag).
2. If the flag is odd, multiply the node with the product.
3. Increase head and flag by 1, and recurse for next nodes.

Below is the implementation of this approach: 

C++

// CPP code to print alternate nodes
// of a linked list using recursion
#include <bits/stdc++.h>
using namespace std;

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

// Inserting node at the beginning
void push(struct Node** head_ref, int new_data)
{
    struct Node* new_node = new Node();
    new_node->data = new_data;
    new_node->next = (*head_ref);
    (*head_ref) = new_node;
}

// Function to find product of alternate
// nodes of linked list.
// The boolean flag isOdd is used to find
// if the current node is even or odd.
void productAlternateNodes(struct Node* node,
                           int& prod, bool isOdd = true)
{
    if (node == NULL)
        return;

    if (isOdd == true)
        prod = prod * (node->data);

    productAlternateNodes(node->next, prod, !isOdd);
}

// Driver code
int main()
{
    // Start with the empty list
    struct Node* head = NULL;

    // construct below list
    // 8 -> 23 -> 11 -> 29 -> 12

    push(&head, 12);
    push(&head, 29);
    push(&head, 11);
    push(&head, 23);
    push(&head, 8);

    int prod = 1;

    productAlternateNodes(head, prod);

    cout << prod;

    return 0;
}

Java

// Java code to print alternate nodes
// of a linked list using recursion
class GFG
{

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

// Inserting node at the beginning
static Node push(Node head_ref, int new_data)
{
    Node new_node = new Node();
    new_node.data = new_data;
    new_node.next = (head_ref);
    (head_ref) = new_node;
    return head_ref;
}
static int prod;

// Function to find product of alternate
// nodes of linked list.
// The boolean flag isOdd is used to find
// if the current node is even or odd.
static void productAlternateNodes(Node node,
                                  boolean isOdd)
{
    if (node == null)
        return;

    if (isOdd == true)
        prod = prod * (node.data);

    productAlternateNodes(node.next, !isOdd);
}

// Driver code
public static void main(String args[])
{

    // Start with the empty list
    Node head = null;

    // construct below list
    // 8 . 23 . 11 . 29 . 12
    head = push(head, 12);
    head = push(head, 29);
    head = push(head, 11);
    head = push(head, 23);
    head = push(head, 8);

    prod = 1;

    productAlternateNodes(head, true);

    System.out.println( prod);
}
}

// This code is contributed by Arnab Kundu

Python3

# Python3 code to print alternate nodes
# of a linked list using recursion

# Link list node
class Node:

    def __init__(self, data):
        self.data = data
        self.next = next

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

    # allocate node
    new_node = Node(0)

    # 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

prod = 1

# Function to find product of alternate
# nodes of linked list.
# The boolean flag isOdd is used to find
# if the current node is even or odd.
def productAlternateNodes(node, isOdd):

    global prod

    if (node == None):
        return

    if (isOdd == True):
        prod = prod * (node.data)

    productAlternateNodes(node.next, not isOdd)

# Driver code

# Start with the empty list
head = None

# construct below list
# 8 -> 23 -> 11 -> 29 -> 12

head = push(head, 12)
head = push(head, 29)
head = push(head, 11)
head = push(head, 23)
head = push(head, 8)

prod = 1

productAlternateNodes(head, True)

print (prod)

# This code is contributed by Arnab Kundu

C#

// C# code to print alternate nodes
// of a linked list using recursion
using System;

class GFG
{

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

// Inserting node at the beginning
static Node push(Node head_ref,
                  int new_data)
{
    Node new_node = new Node();
    new_node.data = new_data;
    new_node.next = (head_ref);
    (head_ref) = new_node;
    return head_ref;
}
static int prod;

// Function to find product of alternate
// nodes of linked list.
// The boolean flag isOdd is used to find
// if the current node is even or odd.
static void productAlternateNodes(Node node,
                                  bool isOdd)
{
    if (node == null)
        return;

    if (isOdd == true)
        prod = prod * (node.data);

    productAlternateNodes(node.next, !isOdd);
}

// Driver code
public static void Main(String []args)
{

    // Start with the empty list
    Node head = null;

    // construct below list
    // 8 . 23 . 11 . 29 . 12
    head = push(head, 12);
    head = push(head, 29);
    head = push(head, 11);
    head = push(head, 23);
    head = push(head, 8);

    prod = 1;

    productAlternateNodes(head, true);

    Console.WriteLine( prod);
}
}

// This code is contributed by Rajput-Ji

Javascript

<script>
// Javascript code to print alternate nodes
// of a linked list using recursion

class Node
{
    constructor()
    {
        this.data = 0;
        this.next = null;
    }
}

// Inserting node at the beginning
function push(head_ref, new_data)
{
    let new_node = new Node();
    new_node.data = new_data;
    new_node.next = (head_ref);
    (head_ref) = new_node;
    return head_ref;
}


let prod;

// Function to find product of alternate
// nodes of linked list.
// The boolean flag isOdd is used to find
// if the current node is even or odd.
function productAlternateNodes(node,isOdd)
{
    if (node == null)
        return;

    if (isOdd == true)
        prod = prod * (node.data);

    productAlternateNodes(node.next, !isOdd);
}

// Driver code
// Start with the empty list
let head = null;

// construct below list
// 8 . 23 . 11 . 29 . 12
head = push(head, 12);
head = push(head, 29);
head = push(head, 11);
head = push(head, 23);
head = push(head, 8);

prod = 1;
productAlternateNodes(head, true);
document.write( prod);

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

Output

1056

Complexity Analysis:

• Time Complexity: O(N)
• Auxiliary Space: O(N)