第一题：

#include <iostream>
#include <queue>
#include <vector>
using namespace std;

int main()
{
int n;
int i, j, k;
int sum;
int avg;
vector<int> start;
int count;
bool flag;
while (cin >> n)
{
sum = 0;
for (i = 0; i < n; i++)
{
cin >> j;
start.push_back(j);
sum += j;
}
if (sum%n != 0)
{
cout << "-1" << endl;
continue;
}
avg = sum/n;
count = 0;
flag = true;
for (i = 0; i < n; i++)
{
if (start[i] > avg && (start[i]-avg)%2 != 0)
{
cout << "-1" << endl;
flag = false;
break;
}
if (start[i] < avg && (avg-start[i])%2 != 0)
{
cout << "-1" << endl;
flag = false;
break;
}
if (start[i] > avg)
{
count += (start[i]-avg)/2;
}
}
if (flag)
{
cout << count << endl;
}
start.clear();
}
return 0; 
}