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 

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 <bits/stdc++.h>
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 <stdio.h>
#include <stdlib.h>

// 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

Javascript

<script>

// JavaScript program to print the difference
// of Alternate Nodes

// Structure of a node of the linked list

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

// Function to get the alternate
// nodes of the linked list
function subtractAlternateNode( head)
{
    let count = 0;
    let 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
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;
    head = head_ref;
}


// Driver Code

// 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);

document.write(subtractAlternateNode(head));

</script>

Output

-15

Time Complexity: O(N), where N is the number of nodes in the linked list
Auxiliary Space: O(1)

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 <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 = (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

    // Construct below 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

    // Construct below 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

Javascript

<script>

// JavaScript code to print difference of
// alternate nodes of a linked list
// using recursion

// A linked list node
class Node
{
    constructor()
    {
        this.data = 0;
        this.next = null;
    }
};

var head= null;;
var difference = 0;

// Inserting node at the beginning
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;
    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.
function subtractAlternateNodes(node, 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
// Start with the empty list
// Construct below 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);
document.write(difference);


</script>

Output

-15

Time Complexity: O(N) where N is number of nodes in the linked list
Auxiliary Space: O(N), for recursion call stack