# 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
```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Iterative Approach :

1. Traverse the whole linked list.
2. Set prod = 1 and count=0.
3. Multiply the data of node with prod when 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 ` `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 ` `#include ` ` `  `/* 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 `

Output:

```1056
```

Recursive Approach:

1. Initialize a static variable(say flag).
2. If flag is odd, multiply the node with 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 ` `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 = (``struct` `Node*)``malloc``(``sizeof``(``struct` `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``; ` ` `  `    ``// con 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 `

## Python

 `# Python 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``; ` ` `  `    ``// con 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 `

Output:

```1056
```

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