Hackerrank - Prepare | Data Structures | Linked Lists | Get Node Value

 This challenge is part of a tutorial track by MyCodeSchool

Given a pointer to the head of a linked list and a specific position, determine the data value at that position. Count backwards from the tail node. The tail is at postion 0, its parent is at 1 and so on.

Example
 refers to 

Each of the data values matches its distance from the tail. The value  is at the desired position.

Function Description

Complete the getNode function in the editor below.

getNode has the following parameters:

• SinglyLinkedListNode pointer head: refers to the head of the list
• int positionFromTail: the item to retrieve

Returns

• int: the value at the desired position

Input Format

The first line contains an integer , the number of test cases.

Each test case has the following format:
The first line contains an integer , the number of elements in the linked list.
The next  lines contains an integer, the data value for an element of the linked list.
The last line contains an integer , the position from the tail to retrieve the value of.

Constraints

• , where  is the  element of the linked list.

Sample Input

2
1
1
0
3
3
2
1
2

Sample Output

1
3

Explanation

In the first case, there is one element in linked list with a value of 1. The last (only) element contains 1.

In the second case, the list is . The element with position of 2 from tail contains 3.

import java.io.*;

import java.math.*;

import java.security.*;

import java.text.*;

import java.util.*;

import java.util.concurrent.*;

import java.util.regex.*;

public class Solution {

    static class SinglyLinkedListNode {

        public int data;

        public SinglyLinkedListNode next;

        public SinglyLinkedListNode(int nodeData) {

            this.data = nodeData;

            this.next = null;

        }

    }

    static class SinglyLinkedList {

        public SinglyLinkedListNode head;

        public SinglyLinkedListNode tail;

        public SinglyLinkedList() {

            this.head = null;

            this.tail = null;

        }

        public void insertNode(int nodeData) {

            SinglyLinkedListNode node = new SinglyLinkedListNode(nodeData);

            if (this.head == null) {

                this.head = node;

            } else {

                this.tail.next = node;

            }

            this.tail = node;

        }

    }

    public static void printSinglyLinkedList(SinglyLinkedListNode node, String sep, BufferedWriter bufferedWriter) throws IOException {

        while (node != null) {

            bufferedWriter.write(String.valueOf(node.data));

            node = node.next;

            if (node != null) {

                bufferedWriter.write(sep);

            }

        }

    }

    

    

    

    

    public static SinglyLinkedListNode insertNodeAtStart(SinglyLinkedListNode revList, int data) {

        SinglyLinkedListNode node = new SinglyLinkedListNode(data);

        node.next = revList;

        return node;

    }

    

    public static int getNode(SinglyLinkedListNode llist, int positionFromTail) {

     SinglyLinkedListNode revList = null;

     SinglyLinkedListNode temp = llist;

     while (temp != null) {

        revList =  insertNodeAtStart(revList, temp.data);

        temp = temp.next;

     }

     

     for (int i = 0; i < positionFromTail; i++) {

         revList = revList.next;

     }

     

     return revList.data;

    }

    private static final Scanner scanner = new Scanner(System.in);