【bzoj4596】黑暗前的幻想乡

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
const int N=20,MOD=1e9+7;
struct xxx{
    int x,y,nxt;
}a[100010];
int A[N][N],h[N],ok[N];
int n,m,tot,ans;
void add(int x,int y,int col);
int solve(int n);
int Abs(int x){return x>0?x:-x;}
bool in(int st,int x){return st>>(x-1)&1;}
int work();

int main(){
#ifndef ONLINE_JUDGE
    freopen("a.in","r",stdin);
#endif
    int x,y;
    scanf("%d",&n);
    memset(h,-1,sizeof(h));
    tot=0;
    for (int i=1;i<n;++i){
        scanf("%d",&m);
        for (int j=1;j<=m;++j){
            scanf("%d%d",&x,&y);
            add(x,y,i);
        }
    }
    ans=0;
    int all=1<<n-1,cnt,tmp,n1;
    for (int i=1;i<all;++i){
        memset(A,0,sizeof(A));
        cnt=0;
        for (int j=1;j<n;++j)
            if (in(i,j)){
                for (int k=h[j];k!=-1;k=a[k].nxt){
                    x=a[k].x; y=a[k].y;
                    ++A[x][x]; ++A[y][y];
                    --A[x][y]; --A[y][x];
                }
            }
            else ++cnt;
        tmp=solve(n-1);
        if (cnt&1) 
            ans=(ans-tmp+MOD)%MOD;
        else 
            ans=(ans+tmp)%MOD;
    }
    printf("%d\n",ans);
}

void add(int x,int y,int col){
    a[++tot].x=x; a[tot].y=y; a[tot].nxt=h[col]; h[col]=tot;
}

int solve(int n){
    int id,ret=1,tmp;
    for (int i=1;i<=n;++i){
        for (id=i;id<=n;++id)
            if (A[id][i]) break;
        if (id>n) continue;
        if (id!=i){
            ret=-ret;
            for (int j=i+1;j<=n;++j) swap(A[i][j],A[id][j]);
        }
        for (int j=i+1;j<=n;++j){
            while (A[j][i]){
                tmp=A[j][i]/A[i][i];
                for (int k=1;k<=n;++k)
                    A[j][k]=(1LL*A[j][k]+MOD-1LL*tmp*A[i][k]%MOD)%MOD;
                if (A[j][i]==0) break;
                ret=-ret;
                for (int k=1;k<=n;++k)
                    swap(A[j][k],A[i][k]);
            }
        }
    }
    for (int i=1;i<=n;++i)
        ret=1LL*ret*A[i][i]%MOD;
    return (ret+MOD)%MOD;
}