whats wrong in code and how to improve
#include <iostream>
using namespace std;
long long int a,i;
int k,n,m;
int main() {
long long int s=0;
cin>>k;
while(k) {
cin>>n;
for(i=0;i<n;i++) {
cin>>a;
m=a%n;
s=s+m;
}
if(s%n==0)
cout<<"YES"<<endl;
else
cout<<"NO"<<endl;
k--;
}
return 0;
}