B. Filya and Homework-Codeforces

B. Filya and Homework-Codeforces

// working.cpp by Bill Weinman <http://bw.org/>
#include <bits/stdc++.h>
using namespace std;
int main()
{
	int n;
	cin>>n;
	vector<int>a(n);
	for(int i=0;i<n;i++)
		cin>>a[i];
	sort(a.begin(),a.end());
	vector<int>::iterator length;
	 length=unique(a.begin(),a.end());
	 a.resize(distance(a.begin(),length));
	if(a.size()<3)
		cout<<"YES"<<endl;
	else if(a.size()==3)
	{
		if(a[0]+a[2]==2*a[1])
			cout<<"YES"<<endl;
		else
			cout<<"NO"<<endl;
	}
	else
		cout<<"NO"<<endl;
	return 0;
}