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>

int num[2000009];

int quicksort(int left,int right)
{
	int i,j,mid;
	i=left;j=right;
	mid=num[(left+right)>>1];
	while (i<j) 
	{
		while (num[i]>mid) ++i;
		while (num[j]<mid) --j;
		if (i<=j)
		{
			int tmp;
			tmp=num[i];num[i]=num[j];num[j]=tmp;
			++i;--j;
		}
	}
	if (i<right) quicksort(i,right);
	if (j>left) quicksort(left,j);
}

main()
{
	int n,i;
	scanf("%d",&n);
	for (i=1;i<=n;i++) 
		scanf("%d",&num[i]);
	quicksort(1,n);
	for (i=2;i<=n;i++)
		if (num[i]==num[i-1])
		{
			printf("NO");
			return 0;
		}
	printf("YES");
	return 0;
}