Find the sum of last n nodes of the linked list

//Find the sum of last n nodes of the linked list

import java.io.*;
import java.util.*;

class Node {
    int data;
    Node next;

    Node(int a) {
        data = a;
        next = null;
    }
}

class Node {
    int data;
    Node next;

    public Node (int data){
        this.data = data;
        this.next = null;
    }
}

class Solution {
    public int sumOfLastN_Nodes(Node head, int n) {
        Node cur = head;
        int size = 0;
        
        while(cur != null) {
            size++;
            cur = cur.next;
        }
        
        int sum = 0;
        
        for(int i = 0; i < size - n; i++) {
            head = head.next;
        }
        
        while(head != null) {
            sum += head.data;
            head = head.next;
        }
        
        return sum;
    }
}

class LinkedList {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int t = Integer.parseInt(br.readLine());

        while(t-- > 0) {
            ArrayList<Integer> arr = new ArrayList<>();
            String input = br.readLine();
            StringTokenizer st = new StringTokenizer(input);

            while(st.hasMoreTokens()) {
                arr.add(Integer.parseInt(st.nextToken()));
            }

            int n = Integer.parseInt(br.readLine());
            Node head = new Node(arr.get(0));
            Node tail = head;

            for(int i = 1; i < arr.size(); ++i) {
                tail.next = new Node(arr.get(i));
                tail = tail.next;
            }

            Solution ob = new Solution();
            System.out.println(ob.sumOfLastN_Nodes(head, n));
        }
    }
}