Sum of nodes in a linked list which are greater than next node

Last Updated : 20 Sep, 2022

Given a linked list, the task is to find the sum of all the nodes which are greater than the node next to them. Note that for the last node of the linked list which doesn’t have any node next to it, it must be greater than the first node in order for it to contribute to the sum.
Examples:

Input: 9 -> 2 -> 3 -> 5 -> 4 -> 6 -> 8
Output: 14
9 + 5 = 14

Input: 2 -> 1 -> 5 -> 7
Output: 9
2 + 7 = 9

Approach: Traverse the whole linked list and for each node, if the node is greater than the next node then add it to the sum. For the last node, compare it to the head of the linked list, if last node is greater than the head then add it to the sum. Print the sum in the end.
Below is the implementation of the above approach:

C++

// C++ implementation of the approach
#include <iostream>
using namespace std;
 
// Represents node of the linked list
struct Node {
    int data;
    Node* next;
};
 
// Function to insert a node at the
// end of the linked list
void insert(Node** root, int item)
{
    Node *ptr = *root, *temp = new Node;
    temp->data = item;
    temp->next = NULL;
 
    if (*root == NULL)
        *root = temp;
    else {
        while (ptr->next != NULL)
            ptr = ptr->next;
        ptr->next = temp;
    }
}
 
// Function to return the sum of the nodes
// which are greater than the node next to them
int sum(Node* root)
{
 
    // If there are no nodes
    if (root == NULL)
        return 0;
 
    int sm = 0;
    Node* ptr = root;
    while (ptr->next != NULL) {
 
        // If the node is greater than the next node
        if (ptr->data > ptr->next->data)
            sm += ptr->data;
        ptr = ptr->next;
    }
 
    // For the last node
    if (ptr->data > root->data)
        sm += ptr->data;
 
    // Return the sum
    return sm;
}
 
// Driver code
int main()
{
    Node* root = NULL;
 
    insert(&root, 9);
    insert(&root, 2);
    insert(&root, 3);
    insert(&root, 5);
    insert(&root, 4);
    insert(&root, 6);
    insert(&root, 8);
 
    cout << sum(root) << endl;
    return 0;
}

Java

// Java implementation of the approach 
class GFG
{
 
// Represents node of the linked list 
static class Node 
{ 
    int data; 
    Node next; 
}; 
 
// Function to insert a node at the 
// end of the linked list 
static Node insert(Node root, int item) 
{ 
    Node ptr = root, temp = new Node(); 
    temp.data = item; 
    temp.next = null; 
 
    if (root == null) 
        root = temp; 
    else
    { 
        while (ptr.next != null) 
            ptr = ptr.next; 
        ptr.next = temp; 
    } 
    return root;
} 
 
// Function to return the sum of the nodes 
// which are greater than the node next to them 
static int sum(Node root) 
{ 
 
    // If there are no nodes 
    if (root == null) 
        return 0; 
 
    int sm = 0; 
    Node ptr = root; 
    while (ptr.next != null) 
    { 
 
        // If the node is greater than the next node 
        if (ptr.data > ptr.next.data) 
            sm += ptr.data; 
        ptr = ptr.next; 
    } 
 
    // For the last node 
    if (ptr.data > root.data) 
        sm += ptr.data; 
 
    // Return the sum 
    return sm; 
} 
 
// Driver code 
public static void main(String args[])
{ 
    Node root = null; 
 
    root=insert(root, 9); 
    root=insert(root, 2); 
    root=insert(root, 3); 
    root=insert(root, 5); 
    root=insert(root, 4); 
    root=insert(root, 6); 
    root=insert(root, 8); 
 
    System.out.print( sum(root) );
}
} 
 
// This code is contributed by Arnab Kundu

Python3

# Python3 implementation of the approach
import math
 
# Represents node of the linked list
class Node: 
    def __init__(self, data): 
        self.data = data 
        self.next = None
 
# Function to root=insert a node at the
# end of the linked list
def insert(root, item):
 
    ptr = root
    temp = Node(item);
    temp.data = item;
    temp.next = None;
     
    if (root == None):
        root = temp;
    else:
        while (ptr.next != None):
            ptr = ptr.next;
        ptr.next = temp;
     
    return root
 
# Function to return the sum of the nodes
# which are greater than the node next to them
def sum(root):
 
    # If there are no nodes
    if (root == None):
        return 0;
 
    sm = 0;
    ptr = root;
    while (ptr.next != None):
 
        # If the node is greater than the next node
        if (ptr.data > ptr.next.data):
            sm += ptr.data;
        ptr = ptr.next;
 
    # For the last node
    if (ptr.data > root.data):
        sm += ptr.data;
 
    # Return the sum
    return sm;
 
# Driver code
if __name__=='__main__': 
    root = None;
    root = insert(root, 9);
    root = insert(root, 2);
    root = insert(root, 3);
    root = insert(root, 5);
    root = insert(root, 4);
    root = insert(root, 6);
    root = insert(root, 8);
 
    print(sum(root))
     
# This code is contributed by Srathore

C#

// C# implementation of the approach
using System;
 
class GFG
{
 
// Represents node of the linked list 
public class Node 
{ 
    public int data; 
    public Node next; 
}; 
 
// Function to insert a node at the 
// end of the linked list 
static Node insert(Node root, int item) 
{ 
    Node ptr = root, temp = new Node(); 
    temp.data = item; 
    temp.next = null; 
 
    if (root == null) 
        root = temp; 
    else
    { 
        while (ptr.next != null) 
            ptr = ptr.next; 
        ptr.next = temp; 
    } 
    return root;
} 
 
// Function to return the sum of the nodes 
// which are greater than the node next to them 
static int sum(Node root) 
{ 
 
    // If there are no nodes 
    if (root == null) 
        return 0; 
 
    int sm = 0; 
    Node ptr = root; 
    while (ptr.next != null) 
    { 
 
        // If the node is greater than the next node 
        if (ptr.data > ptr.next.data) 
            sm += ptr.data; 
        ptr = ptr.next; 
    } 
 
    // For the last node 
    if (ptr.data > root.data) 
        sm += ptr.data; 
 
    // Return the sum 
    return sm; 
} 
 
// Driver code 
public static void Main(String []args)
{ 
    Node root = null; 
 
    root = insert(root, 9); 
    root = insert(root, 2); 
    root = insert(root, 3); 
    root = insert(root, 5); 
    root = insert(root, 4); 
    root = insert(root, 6); 
    root = insert(root, 8); 
 
    Console.Write( sum(root) );
}
}
 
// This code contributed by Rajput-Ji

Javascript

<script>
 
// Javascript implementation of the approach
 
// Represents node of the linked list
class Node {
        constructor() {
                this.data = 0;
                this.next = null;
             }
        }
         
// Function to insert a node at the
// end of the linked list
function insert( root, item)
{
    var ptr = root, temp = new Node();
    temp.data = item;
    temp.next = null;
 
    if (root == null)
        root = temp;
    else
    {
        while (ptr.next != null)
            ptr = ptr.next;
        ptr.next = temp;
    }
    return root;
}
 
// Function to return the sum of the nodes
// which are greater than the node next to them
function sum( root)
{
 
    // If there are no nodes
    if (root == null)
        return 0;
 
    let sm = 0;
    var ptr = root;
    while (ptr.next != null)
    {
 
        // If the node is greater than the next node
        if (ptr.data > ptr.next.data)
            sm += ptr.data;
        ptr = ptr.next;
    }
 
    // For the last node
    if (ptr.data > root.data)
        sm += ptr.data;
 
    // Return the sum
    return sm;
}
 
 
// Driver Code
var root = null;
 
root=insert(root, 9);
root=insert(root, 2);
root=insert(root, 3);
root=insert(root, 5);
root=insert(root, 4);
root=insert(root, 6);
root=insert(root, 8);
 
document.write( sum(root) );
 
// This code is contributed by jana_sayantan.
</script>

Output:

Time complexity: O(n) where n is the size of the linked list
Auxiliary Space: O(1)

Sum of the alternate nodes of linked list

Premdeep Toppo

Improve

Sum of nodes in a linked list which are greater than next node

C++

Java

Python3

C#

Javascript

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