# Subtraction of the alternate nodes of Linked List

Given a linked list. The task is to print the difference between the first odd positioned node with the sum of all other odd positioned nodes.

Examples:

Input : 1 -> 8 -> 3 -> 10 -> 17 -> 22 -> 29 -> 42
Output : -48
Alternate nodes : 1 -> 3 -> 17 -> 29
1 – (3 + 17 + 29) = -48

Input : 10 -> 17 -> 33 -> 38 -> 73
Output : -96
Alternate nodes : 10 -> 33 -> 73
10 – (33 + 73) = -96

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

We have already discussed the sum of the alternative nodes of a linked list

Iterative Approach :

1. Traverse the whole linked list.
2. Set difference = 0 and count=0.
3. Subtract the data of node from difference when count is even.
4. Visit the next node.

Below is the implementation of the above approach:

## C++

 `// C++ program to print the difference  ` `// of Alternate Nodes  ` `#include ` `using` `namespace` `std; ` ` `  `// Link list node  ` `struct` `Node {  ` `    ``int` `data;  ` `    ``struct` `Node* next;  ` `};  ` ` `  `// Function to get the alternate  ` `// nodes of the linked list  ` `int` `subtractAlternateNode(``struct` `Node* head)  ` `{  ` `    ``int` `count = 0;  ` `    ``int` `difference = 0;  ` ` `  `    ``while` `(head != NULL) {  ` ` `  `        ``// When count is even subtract the nodes  ` `        ``if` `(count % 2 == 0) ` `            ``if` `(difference == 0){ ` `                ``difference = head->data; ` `            ``} ` `            ``else``{ ` `                ``difference -= head->data;  ` `            ``}  ` `        ``// Count the nodes  ` `        ``count++;  ` ` `  `        ``// Move on the next node.  ` `        ``head = head->next;  ` `    ``}  ` `    ``return` `difference;  ` `}  ` ` `  `// 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 << subtractAlternateNode(head);  ` `    ``return` `0;  ` `} ` ` `  `// This code is contributed by shubhamsingh10 `

## C

 `// C program to print the difference  ` `// of Alternate Nodes  ` `#include   ` `#include   ` `   `  `// Link list node  ` `struct` `Node {  ` `    ``int` `data;  ` `    ``struct` `Node* next;  ` `};  ` `   `  `// Function to get the alternate   ` `// nodes of the linked list  ` `int` `subtractAlternateNode(``struct` `Node* head)  ` `{  ` `    ``int` `count = 0;  ` `    ``int` `difference = 0;  ` `   `  `    ``while` `(head != NULL) {  ` `   `  `        ``// When count is even subtract the nodes  ` `        ``if` `(count % 2 == 0) ` `            ``if` `(difference == 0){ ` `                ``difference = head->data; ` `            ``} ` `            ``else``{ ` `                ``difference -= head->data;  ` `            ``}   ` `        ``// Count the nodes  ` `        ``count++;  ` `   `  `        ``// Move on the next node.  ` `        ``head = head->next;  ` `    ``}  ` `    ``return` `difference;  ` `}  ` `   `  `// 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 "``, subtractAlternateNode(head));  ` `    ``return` `0;  ` `} `

## Java

 `// Java program to print the difference  ` `// of Alternate Nodes  ` `import` `java.util.*; ` ` `  `class` `GFG  ` `{ ` `     `  `static` `Node head; ` `// Link list node  ` `static` `class` `Node  ` `{  ` `    ``int` `data;  ` `    ``Node next;  ` `};  ` `     `  `// Function to get the alternate  ` `// nodes of the linked list  ` `static` `int` `subtractAlternateNode(Node head)  ` `{  ` `    ``int` `count = ``0``;  ` `    ``int` `difference = ``0``;  ` `     `  `    ``while` `(head != ``null``)  ` `    ``{  ` `     `  `        ``// When count is even subtract the nodes  ` `        ``if` `(count % ``2` `== ``0``) ` `            ``if` `(difference == ``0``) ` `            ``{ ` `                ``difference = head.data; ` `            ``} ` `            ``else` `            ``{ ` `                ``difference -= head.data;  ` `            ``}  ` `             `  `        ``// Count the nodes  ` `        ``count++;  ` `     `  `        ``// Move on the next node.  ` `        ``head = head.next;  ` `    ``}  ` `    ``return` `difference;  ` `}  ` `     `  `// Function to push node at head  ` `static` `void` `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;  ` `    ``head = head_ref; ` `}  ` `     `  `// Driver code  ` `public` `static` `void` `main(String[] args)  ` `{ ` `    ``// Start with the empty list  ` `    ``head = ``null``;  ` `     `  `    ``// Use push() function to con  ` `    ``// the below list 8 . 23 . 11 . 29 . 12  ` `    ``push(head, ``12``);  ` `    ``push(head, ``29``);  ` `    ``push(head, ``11``);  ` `    ``push(head, ``23``);  ` `    ``push(head, ``8``);  ` `     `  `    ``System.out.printf(``" %d "``, subtractAlternateNode(head)); ` `} ` `} ` ` `  `// This code is contributed by Princi Singh `

## Python3

 `# Python3 program to print the difference  ` `# of Alternate Nodes  ` `import` `math  ` ` `  `# Link list node  ` `class` `Node:  ` `    ``def` `__init__(``self``, data):  ` `        ``self``.data ``=` `data  ` `        ``self``.``next` `=` `None` ` `  `# Function to get the alternate  ` `# nodes of the linked list  ` `def` `subtractAlternateNode(head):  ` `    ``count ``=` `0` `    ``difference ``=` `0` `     `  `    ``while` `(head !``=` `None``) :  ` `     `  `        ``# When count is even subtract the nodes  ` `        ``if` `(count ``%` `2` `=``=` `0``): ` `            ``if` `(difference ``=``=` `0``): ` `                ``difference ``=` `head.data ` `             `  `            ``else``: ` `                ``difference ``=` `difference ``-` `head.data  ` `             `  `        ``# Count the nodes  ` `        ``count ``=` `count ``+` `1` `     `  `        ``# Move on the next node.  ` `        ``head ``=` `head.``next` `     `  `    ``return` `difference  ` `     `  `# Function to 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``(subtractAlternateNode(head)) ` `     `  `# This code is contributed by Srathore `

## C#

 `// C# program to print the difference  ` `// of Alternate Nodes  ` `using` `System; ` `     `  `class` `GFG  ` `{ ` `     `  `static` `Node head; ` ` `  `// Link list node  ` `public` `class` `Node  ` `{  ` `    ``public` `int` `data;  ` `    ``public` `Node next;  ` `};  ` `     `  `// Function to get the alternate  ` `// nodes of the linked list  ` `static` `int` `subtractAlternateNode(Node head)  ` `{  ` `    ``int` `count = 0;  ` `    ``int` `difference = 0;  ` `     `  `    ``while` `(head != ``null``)  ` `    ``{  ` `     `  `        ``// When count is even subtract the nodes  ` `        ``if` `(count % 2 == 0) ` `            ``if` `(difference == 0) ` `            ``{ ` `                ``difference = head.data; ` `            ``} ` `            ``else` `            ``{ ` `                ``difference -= head.data;  ` `            ``}  ` `             `  `        ``// Count the nodes  ` `        ``count++;  ` `     `  `        ``// Move on the next node.  ` `        ``head = head.next;  ` `    ``}  ` `    ``return` `difference;  ` `}  ` `     `  `// Function to push node at head  ` `static` `void` `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;  ` `    ``head = head_ref; ` `}  ` `     `  `// Driver code  ` `public` `static` `void` `Main(String[] args)  ` `{ ` `    ``// Start with the empty list  ` `    ``head = ``null``;  ` `     `  `    ``// Use push() function to con  ` `    ``// the below list 8 . 23 . 11 . 29 . 12  ` `    ``push(head, 12);  ` `    ``push(head, 29);  ` `    ``push(head, 11);  ` `    ``push(head, 23);  ` `    ``push(head, 8);  ` `     `  `    ``Console.WriteLine(``" {0} "``,  ` `            ``subtractAlternateNode(head)); ` `} ` `} ` ` `  `// This code is contributed by PrinciRaj1992  `

Output:

`-15`

Recursive Approach :

1. Initialize a static variable(say flag).
2. If flag is odd, subtract the node from difference.
3. increase head and flag by 1, and recurse for next nodes.

Below is the implementation of the above approach:

## C++

 `// CPP code to print difference of 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 difference of alternate ` `// nodes of linked list. ` `// The boolean flag isOdd is used to find ` `// if the current node is even or odd. ` `void` `subtractAlternateNodes(``struct` `Node* node, ` `                 ``int``& difference, ``bool` `isOdd = ``true``) ` `{ ` `    ``if` `(node == NULL) ` `        ``return``; ` ` `  `    ``if` `(isOdd == ``true``) { ` `        ``if` `(difference == 0) { ` `            ``difference = node->data; ` `        ``} ` `        ``else` `{ ` `            ``difference = difference - (node->data); ` `        ``} ` `    ``} ` `    ``subtractAlternateNodes(node->next, difference,  ` `                                            ``!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` `difference = 0; ` ` `  `    ``subtractAlternateNodes(head, difference); ` ` `  `    ``cout << difference; ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java code to print difference of  ` `// alternate nodes of a linked list  ` `// using recursion ` `class` `GFG  ` `{ ` ` `  `// A linked list node ` `static` `class` `Node  ` `{ ` `    ``int` `data; ` `    ``Node next; ` `}; ` `static` `Node head;  ` `static` `int` `difference; ` ` `  `// 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; ` `    ``head = head_ref; ` `    ``return` `head; ` `} ` ` `  `// Function to find difference of alternate ` `// nodes of linked list. ` `// The boolean flag isOdd is used to find ` `// if the current node is even or odd. ` `static` `void` `subtractAlternateNodes(Node node,  ` `                                   ``boolean` `isOdd) ` `{ ` `    ``if` `(node == ``null``) ` `        ``return``; ` ` `  `    ``if` `(isOdd == ``true``)  ` `    ``{ ` `        ``if` `(difference == ``0``)  ` `        ``{ ` `            ``difference = node.data; ` `        ``} ` `        ``else` `        ``{ ` `            ``difference = difference - (node.data); ` `        ``} ` `    ``} ` `    ``subtractAlternateNodes(node.next, !isOdd); ` `} ` ` `  `// Driver code ` `public` `static` `void` `main(String[] args)  ` `{ ` `    ``// Start with the empty list ` ` `  `    ``// Conbelow list ` `    ``// 8 -> 23 -> 11 -> 29 -> 12 ` ` `  `    ``push(head, ``12``); ` `    ``push(head, ``29``); ` `    ``push(head, ``11``); ` `    ``push(head, ``23``); ` `    ``push(head, ``8``); ` ` `  `    ``difference = ``0``; ` ` `  `    ``subtractAlternateNodes(head, ``true``); ` `    ``System.out.println(difference); ` `} ` `} ` ` `  `// This code is contributed by PrinciRaj1992  `

## Python

 `# Python code to print difference of 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 ` `     `  `difference ``=` `0``; ` ` `  `# Function to find difference of alternate ` `# nodes of linked list. ` `# The boolean flag isOdd is used to find ` `# if the current node is even or odd. ` `def` `subtractAlternateNodes(node, isOdd ): ` ` `  `    ``global` `difference ` `     `  `    ``if` `(node ``=``=` `None``): ` `        ``return``; ` ` `  `    ``if` `(isOdd ``=``=` `True``):  ` `        ``if` `(difference ``=``=` `0``) : ` `            ``difference ``=` `node.data; ` `         `  `        ``else` `: ` `            ``difference ``=` `difference ``-` `(node.data); ` `         `  `    ``subtractAlternateNodes(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``); ` ` `  `difference ``=` `0``; ` ` `  `subtractAlternateNodes(head, ``True``); ` ` `  `print``( difference); ` ` `  `# This code is contributed by Arnab Kundu `

## C#

 `// C# code to print difference of  ` `// 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; ` `}; ` `static` `Node head;  ` `static` `int` `difference; ` ` `  `// 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; ` `    ``head = head_ref; ` `    ``return` `head; ` `} ` ` `  `// Function to find difference of alternate ` `// nodes of linked list. ` `// The boolean flag isOdd is used to find ` `// if the current node is even or odd. ` `static` `void` `subtractAlternateNodes(Node node,  ` `                                   ``Boolean isOdd) ` `{ ` `    ``if` `(node == ``null``) ` `        ``return``; ` ` `  `    ``if` `(isOdd == ``true``)  ` `    ``{ ` `        ``if` `(difference == 0)  ` `        ``{ ` `            ``difference = node.data; ` `        ``} ` `        ``else` `        ``{ ` `            ``difference = difference - (node.data); ` `        ``} ` `    ``} ` `    ``subtractAlternateNodes(node.next, !isOdd); ` `} ` ` `  `// Driver code ` `public` `static` `void` `Main(String[] args)  ` `{ ` `    ``// Start with the empty list ` ` `  `    ``// Conbelow list ` `    ``// 8 -> 23 -> 11 -> 29 -> 12 ` ` `  `    ``push(head, 12); ` `    ``push(head, 29); ` `    ``push(head, 11); ` `    ``push(head, 23); ` `    ``push(head, 8); ` ` `  `    ``difference = 0; ` ` `  `    ``subtractAlternateNodes(head, ``true``); ` `    ``Console.WriteLine(difference); ` `} ` `} ` ` `  `// This code is contributed by Rajput-Ji `

Output:

`-15`

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