题解 | 元素方碑

#include <iostream>
using namespace std;

int main() {
    int t;
    cin >> t;
    while (t--)
    {
        int n;
        cin >> n;
        int sumn = 0;
        int sumeven = 0;
        int sumodd = 0;
        int a;
        for (int i = 0; i < n; i++)
        {
            cin >> a;
            sumn += a;
            if (i % 2 == 0)
            {
                sumeven += a;
            }
            else
            {
                sumodd += a;
            }
        }

        int evennum = n / 2 + n % 2;
        int evenodd = n / 2;
        if ((sumn % n == 0) && (sumodd * evennum) == (evenodd * sumeven))
        {
            cout << "YES" << endl;
        }
        else
        {
            cout << "NO" << endl;
        }
    }
}