指针访问元素

#include<iostream>
#include<cmath>
#include<algorithm>
#include<cstring>
#include<string>
#include<stack>
#include<queue>
#include<map>
#include<cstdlib>
#include<set>
#include<ctime>
#include<vector>
#include<cstdio>
#include<list>
using namespace std;
typedef long long ll;
int INF=2147483647;
int inf=-2147483648;
#define read(x) scanf("%d",&x);
#define fo(i,n) for(int i=1;i<=(n);i++)
#define me(a) memset(a,0,sizeof(a));
#define one(x) cout<<(x)<<endl;
#define two(a,b) cout<<(a)<<" "<<(b)<<endl;
int a[100005];
int main()
{
    ios::sync_with_stdio(false);
    int n;
    cin>>n;
    set<int>q;
    for(int i=0;i<n;i++)
    {
        cin>>a[i];
        q.insert(a[i]);
    }
    if(q.size()<=2)
    {
        one("YES");
    }
    else if(q.size()>3)
    {
        one("NO");
    }
    else
    {
        int a=*q.begin();
        int b=*(++q.begin());
        int c=*(++++q.begin());
        if(c-b==b-a)
        {
            one("YES");
        }
        else
        {
            one("NO");
        }
    }
    return 0;
}