[SHOI2016] 黑暗前的幻想乡 - 矩阵树定理,容斥

#include 
using namespace std;
#define int long long
const int N = 20;
const int mod = 1e+9 + 7;
namespace mat {
int a[N][N];
int n,p=1;
void Clear() {
    memset(a,0,sizeof a);
}
int Solve() {
    int ans = 1;
    for(int i = 1; i < n; i ++) {
        for(int j = i + 1; j < n; j ++)
            while(a[j][i]) {
                int t = a[i][i] / a[j][i];
                for(int k = i; k < n; k ++)
                    a[i][k] = (a[i][k] - t * a[j][k] + mod) % mod;
                swap(a[i], a[j]);
                ans = - ans;
            }
        ans = (ans * a[i][i]) % mod;
    }
    return (ans + mod) % mod;
}
void Make(int p,int q) {
    a[p][q]--;
    a[q][p]--;
    a[p][p]++;
    a[q][q]++;
}
} // namespace mat
int n;
vector  > v[N];
signed main() {
    ios::sync_with_stdio(false);
    cin>>n;
    for(int i=1;i>t;
        for(int j=1;j<=t;j++) {
            int t1,t2;
            cin>>t1>>t2;
            v[i].push_back(make_pair(t1,t2));
        }
    }
    int ans = 0;
    mat::n=n;
    for(int i=0;i<1<<(n-1);i++) {
        int t=__builtin_popcount(i);
        mat::Clear();
        for(int j=1;j<=(n-1);j++) {
            if(i&(1<<(j-1))) {
                for(int k=0;k