Codeforces_714_B

http://codeforces.com/problemset/problem/714/B

当不同大小整数有1、2个时，肯定成立，3个时，需要判断，大于等于4个，则肯定不成立。

#include <algorithm>
#include <iostream>
#include <cstdio>
using namespace std;


long long a [5];
int main()
{
    int n;
    cin >> n;
    int num = 0;
    while(n--)
    {
        if(num > 3)
        {
            break;
        }
        long long temp;
        cin >> temp;
        int flag = 1;
        for(int i = 0;i < num;i++)
        {
            if(a[i] == temp)    flag = 0;
        }
        if(flag) a[num++] = temp;
    }
    if(num == 1 || num == 2)    printf("YES
");
    else if(num == 3)
    {
        sort(a,a+3);
        if(a[0]+a[2] == 2*a[1]) printf("YES
");
        else    printf("NO
");
    }
    else
    {
        printf("NO
");
    }

    return 0;
}