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 C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <queue>
#include <map>
#include <cmath>
#include <numeric>
#include <iomanip>
#include <set>
#include <string.h>

using namespace std;

typedef long long ll;

#define REP(i,n) for(ll (i)=0;(i)<(n);(i)++)
#define REP3(i,st,en) for(ll (i)=(st);(i)<(en);(i)++)

using P = pair<ll, ll>;
const int MOD = 1e9+7;
const ll INF = 1e+14;
const double PI = 3.14159265349;



int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  ll N;
  cin >> N;
  vector<ll> A(N);
  REP(i,N) { cin >> A[i]; }

  set<ll> seen;
  REP(i,N) {
    if (seen.find(A[i]) != seen.end()){
      cout << "NO" << "\n";
      return 0;
    }
    seen.insert(A[i]);
  }

  cout << "YES" << "\n";
  return 0;
}