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: Time Limit Exceeded)

#include<bits/stdc++.h>
using namespace std;
#define rep(i, n) for(int i=0; i<n; i++)
typedef unsigned long long ull;
typedef pair<int, int> P;
 
int main(){
  long n;
  cin >> n;
  vector<long> a(n);
  bool IsNotUnique = false;
  
  for(int i=0; i<n; i++){
    cin >> a[i];
  }

  for(int i=0; i<n-1; i++){
    for(int j=i+1; j<n; j++){
      if(a[i]==a[j]){
        IsNotUnique = true;
        break;
      }
    }
    if(IsNotUnique) break;
  }
 
  if(IsNotUnique)  cout << "NO" << endl;
  else             cout << "YES" << endl;
 
  return 0;
}