#include <cstdio>
#include <iostream>
#include <cstdlib>
#include <vector>
#define f(i,a,b) for(int i=a;i<b;++i)
using namespace std;
int main()
{ int t; cin>>t;
f(i,0,t)
{ int k=2;int tam;cin>>tam;
vector<int> v(tam);
f(j,0,tam)
cin>>v[j];
if (tam==1)
k=-1;
else
{ int c=v[0]-v[1];
f(r,0,tam-1)
{ if (v[r]-v[r+1]!=c) {k--;break;}
}
f(r,0,tam-1)
{ if (v[r]*v[1]!=v[r+1]*v[0]) {k--;break;}
}
}
if (k==2&&v[0]==v[1]) k=1;
cout<<k<<endl;
}
return 0;
}
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