Problem:
Score : 300 points

Problem Statement

Given is a sequence of integers A_1, A_2, ..., A_N.
If its elements are pairwise distinct, print YES; otherwise, print NO.

Constraints

2 ≤ N ≤ 200000

1 ≤ A_i ≤ 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_1 ... A_N

Output

If the elements of the sequence are pairwise distinct, print YES; otherwise, print NO.

Sample Input 1

5
2 6 1 4 5

Sample Output 1

YES

The elements are pairwise distinct.

Sample Input 2

6
4 1 3 1 6 2

Sample Output 2

NO

The second and fourth elements are identical.

Sample Input 3

2
10000000 10000000

Sample Output 3

NO

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String line = sc.nextLine();

        int num = Integer.parseInt(line);
        String[] elementStr = sc.nextLine().split(" ");

        ArrayList <Integer> elem = new ArrayList<Integer>();
        //Integer[] elem = new Integer[num];
        for(int i = 0; i < num ;i++) {
        	elem.add(Integer.parseInt(elementStr[i]));
        }
        Collections.sort(elem);
        boolean distinction = true;
        for(int i = 0; i < elem.size()-1; i++) {
        	if(elem.get(i) == elem.get(i + 1)) {
        		distinction = false;
        		break;
        	}
        }

        if(distinction) {
        	System.out.println("YES");
        }else {
        	System.out.println("NO");
        }
    }
}