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: Accepted)

/*
    Those who cannot remember the past are condemned to repeat it.
                                            - Dynamic Programming
    
    I never lose, I either win or I learn.
                - Competitive Programming

*/

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.HashSet;
import java.util.StringTokenizer;

public class Main {
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st;
        PrintWriter pw = new PrintWriter(System.out);

        HashSet<Integer> hs = new HashSet<>();
        int n = Integer.parseInt(br.readLine());

        boolean dis = true;
        st = new StringTokenizer(br.readLine());
        for(int i=0 ; i<n ; i++) {
            int x = Integer.parseInt(st.nextToken());
            if(hs.contains(x)) {
                dis = false;
                break;
            }
            else {
                hs.add(x);
            }
        }

        if(dis) pw.println("YES");
        else pw.println("NO");
        
        
        
        
        
        
        pw.flush();
        pw.close();
    }
}