Sum of the alternate nodes of linked list

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

Examples:

Input : 1 -> 8 -> 3 -> 10 -> 17 -> 22 -> 29 -> 42
Output : 50
Alternate nodes : 1 -> 3 -> 17 -> 29

Input : 10 -> 17 -> 33 -> 38 -> 73
Output : 116
Alternate nodes : 10 -> 33 -> 73

Iterative Approach :

  1. Traverse the whole linked list.
  2. Set sum = 0 and count=0.
  3. Add the data of node to sum when count is even.
  4. Visit the next node.

Below is the implementation of this approach:

C

filter_none

edit
close

play_arrow

link
brightness_4
code

// C code to print the sum 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 sumAlternateNode(struct Node* head)
{
    int count = 0;
    int sum = 0;
  
    while (head != NULL) {
  
        // when count is even sum the nodes
        if (count % 2 == 0)
            sum += head->data;
  
        // count the nodes
        count++;
  
        // move on the next node.
        head = head->next;
    }
    return sum;
}
  
// 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 ", sumAlternateNode(head));
    return 0;
}

chevron_right


Java

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java code to print the sum 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 sumAlternateNode( Node head) 
    int count = 0
    int sum = 0
  
    while (head != null
    
  
        // when count is even sum the nodes 
        if (count % 2 == 0
            sum += head.data; 
  
        // count the nodes 
        count++; 
  
        // move on the next node. 
        head = head.next; 
    
    return sum; 
  
// 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 ", sumAlternateNode(head)); 
}
  
// This code is contributed by Arnab Kundu

chevron_right


C#

filter_none

edit
close

play_arrow

link
brightness_4
code

// C# code to print the sum 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 sumAlternateNode( Node head) 
    int count = 0; 
    int sum = 0; 
  
    while (head != null
    
  
        // when count is even sum the nodes 
        if (count % 2 == 0) 
            sum += head.data; 
  
        // count the nodes 
        count++; 
  
        // move on the next node. 
        head = head.next; 
    
    return sum; 
  
// 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} ", sumAlternateNode(head)); 
  
// This code has been contributed by 29AjayKumar

chevron_right


Output:

31

Recursive Approach :

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

Below is the implementation of this approach:

C++

filter_none

edit
close

play_arrow

link
brightness_4
code

// CPP code to print sum 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 sum 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& sum, bool isOdd = true)
{
    if (node == NULL)
        return;
  
    if (isOdd == true)
        sum = sum + (node->data);
  
    productAlternateNodes(node->next, sum, !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 sum = 0;
  
    productAlternateNodes(head, sum);
  
    cout << sum;
  
    return 0;
}

chevron_right


Java

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java code to print sum of alternate nodes
// of a linked list using recursion
  
class GFG 
{
      
// Start with the empty list 
static Node head=null
  
static int sum;
  
// 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=head_ref;
}
  
// Function to find sum 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)
        sum = sum + (node.data);
  
    productAlternateNodes(node.next, !isOdd);
}
  
// Driver code
public static void main(String[] args) 
{
    // conbelow list
    // 8 . 23 . 11 . 29 . 12
  
    push(head, 12);
    push(head, 29);
    push(head, 11);
    push(head, 23);
    push(head, 8);
  
    sum = 0;
  
    productAlternateNodes(head,true);
  
    System.out.println(sum);
}
}
  
/* This code is contributed by PrinciRaj1992 */

chevron_right


C#

filter_none

edit
close

play_arrow

link
brightness_4
code

// C# code to print sum of alternate nodes
// of a linked list using recursion
using System; 
      
class GFG 
{
      
// Start with the empty list 
static Node head = null
  
static int sum;
  
// 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=head_ref;
}
  
// Function to find sum 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)
        sum = sum + (node.data);
  
    productAlternateNodes(node.next, !isOdd);
}
  
// Driver code
public static void Main(String[] args) 
{
    // conbelow list
    // 8 -> 23 -> 11 -> 29 -> 12
  
    push(head, 12);
    push(head, 29);
    push(head, 11);
    push(head, 23);
    push(head, 8);
  
    sum = 0;
  
    productAlternateNodes(head,true);
  
    Console.WriteLine(sum);
}
}
  
// This code is contributed by Rajput-Ji

chevron_right


Output:

31


My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.