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: Wrong Answer)

#include <stdio.h>
int cmp(const void *a, const void *b)
{
 	return *(int*)a - *(int*)b;
 }
int main()
{
	int n;
	scanf("%d",&n);
	int a[n];
	int i;
	for(i=0;i<n;i++){
		scanf("%d",&a[i]);
	}
	qsort(a,n,sizeof(a[0]),cmp);
	int flag=0;
	if(n/2!=0){
		for(i=0;i<n/2;i++){
			if(a[i]+a[n-i-2]!=a[n-1]){
				flag=1;
				break;
			}
		}
		if(flag) printf("NO");
		else printf("YES");
	}
	else{
		for(i=1;i<n/2;i++){
			if(a[i]+a[n-i-1]!=a[0]+a[n-1]){
				flag=1;
				break;
			}
		if(flag) printf("NO");
		else printf("YES");
		}
	}
	return 0;
}