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>

typedef int value_type;
 
value_type med3(value_type x, value_type y, value_type 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(value_type a[], int left, int right) {
    if (left < right) {
        int i = left, j = right;
        value_type 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 n, a[200001];
  int i, flag = 0;

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

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