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 (GCC 5.4.1) (judge verdict: Accepted)

#include<stdio.h>
#include<string.h>

int up(const void *a , const void *b){
  return *(int *)a - *(int *)b;
}

int main(void){
  int n;
  scanf("%d",&n);

  int  a[n];
  for(int i = 0;i < n;i ++){
    scanf("%d",&a[i]);
  }

  qsort(a,n,sizeof(int),up);
  int flag = 0;
  for(int i = 0;i < n - 1;i ++){
    if(a[i] == a[i + 1]){
      flag = 1;
      i += n;
    }
  }
  if(flag == 0){
  printf("YES\n");
  }
  else{
    printf("NO\n");
  }
  return 0;
}