LonelyInteger.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 LonelyInteger {
//	https://www.hackerrank.com/challenges/lonely-integer/problem
    // Complete the lonelyinteger function below.
    static int lonelyinteger(int[] a) {
        List<Integer> list = new ArrayList();
        for (Integer i : a) {
            list.add(i);
        }
        
        for(int i = 0; i<list.size();i++) {
           if(i == list.lastIndexOf(list.get(i)) && i == list.indexOf(list.get(i)))
                return list.get(i);
        }
        return -1;
    }

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

        int[] a = new int[n];

        String[] aItems = scanner.nextLine().split(" ");
        scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");

        for (int i = 0; i < n; i++) {
            int aItem = Integer.parseInt(aItems[i]);
            a[i] = aItem;
        }

        int result = lonelyinteger(a);

        bufferedWriter.write(String.valueOf(result));
        bufferedWriter.newLine();

        bufferedWriter.close();

        scanner.close();
    }
}