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>
#include <stdlib.h>

int med3(int x, int y, int z)
{
  if (x < y)
  if (y < z) return y; else if (z < x) return x; else return z; else
  if (z < y) return y; else if (x < z) return x; else return z;
}

void QuickSort(int a[], int left, int right)
{
  if (left < right) {
    int i = left, j = right;
    int tmp, pivot = med3(a[i], a[i + (j - i) / 2], a[j]);
    while (1) {
      while (a[i] < pivot) 
      i++;
      while (pivot < a[j])
      j--;
      if (i >= j) break;
      tmp = a[i];
      a[i] = a[j];
      a[j] = tmp;
      i++;
      j--;
    }
    QuickSort(a, left, i - 1);
    QuickSort(a, j + 1, right);
  }
}

int main (void)
{
  int ar[200000];
  int len;
  scanf("%d", &len);
  for (int i = 0; i < len; i++){
    scanf("%d", &(ar[i]));
  }
  QuickSort(ar, 0, len - 1);
  for(int j = 0; j <= len - 2; j++){
    if (ar[j] == ar[j + 1]){
    puts("NO");
      exit(0);
    }
  }
  puts("YES");
  return 0;
}