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

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// 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; 
}

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Java

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// 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

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C#

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// 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 

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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++

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// 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;
}

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Java

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// 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 

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C#

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// 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

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Output:

-15


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