ReverseLinkedListPer.java

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);
            }
        }
    }

    // Complete the reverse function below.

    /*
     * For your reference:
     *
     * SinglyLinkedListNode {
     *     int data;
     *     SinglyLinkedListNode next;
     * }
     *
     */
    static SinglyLinkedListNode reverse(SinglyLinkedListNode head) 
    {
          
          SinglyLinkedListNode temp = head;  //to determine the current node..
          SinglyLinkedListNode next = null;
          SinglyLinkedListNode pre = null;
          while(temp!=null) //traverse till the end..
          {
              next = temp.next;
              temp.next = pre;
              pre = temp;
              temp = next;
          }
         head = pre;
         return head;
    }

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

    public static void main(String[] args) throws IOException {
        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));

        int tests = scanner.nextInt();
        scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");

        for (int testsItr = 0; testsItr < tests; testsItr++) {
            SinglyLinkedList llist = new SinglyLinkedList();

            int llistCount = scanner.nextInt();
            scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");

            for (int i = 0; i < llistCount; i++) {
                int llistItem = scanner.nextInt();
                scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");

                llist.insertNode(llistItem);
            }

            SinglyLinkedListNode llist1 = reverse(llist.head);

            printSinglyLinkedList(llist1, " ", bufferedWriter);
            bufferedWriter.newLine();
        }

        bufferedWriter.close();

        scanner.close();
    }
}