SP104 Highways （矩阵树，高斯消元）

矩阵树定理裸题

//#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#define R(a,b,c) for(register int  a = (b); a <= (c); ++ a)
#define nR(a,b,c) for(register int  a = (b); a >= (c); -- a)
#define Max(a,b) ((a) > (b) ? (a) : (b))
#define Min(a,b) ((a) < (b) ? (a) : (b))
#define Fill(a,b) memset(a, b, sizeof(a))
#define Abs(a) ((a) < 0 ? -(a) : (a))
#define Swap(a,b) a^=b^=a^=b
#define ll long long

#define ON_DEBUG

#ifdef ON_DEBUG

#define D_e_Line printf("

----------

")
#define D_e(x)  cout << #x << " = " << x << endl
#define Pause() system("pause")
#define FileOpen() freopen("in.txt","r",stdin);

#else

#define D_e_Line ;
#define D_e(x)  ;
#define Pause() ;
#define FileOpen() ;

#endif

struct ios{
    template<typename ATP>ios& operator >> (ATP &x){
        x = 0; int f = 1; char c;
        for(c = getchar(); c < '0' || c > '9'; c = getchar()) if(c == '-')  f = -1;
        while(c >= '0' && c <= '9') x = x * 10 + (c ^ '0'), c = getchar();
        x*= f;
        return *this;
    }
}io;
using namespace std;

const int N = 17;
const double eps = 1e-8;

int n;
double a[N][N];
inline void Gauss(){
	--n;
	R(i,1,n){
		int r = i;
		R(j,i + 1,n){
			if(fabs(a[j][i]) > fabs(a[r][i])){
				r = j;
			}
		}
		if(fabs(a[r][i]) < eps){
			printf("0
");
			return;
		}
		if(r != i){
			R(j,1,n)
				swap(a[r][j], a[i][j]);
		}
		R(j,i + 1,n){
			double t = a[j][i] / a[i][i];
			R(k,i,n){
				a[j][k] -= t * a[i][k];
			}
		}
	}
	double ans = 1;
	R(i,1,n){
		ans *= a[i][i];
	}
	printf("%.0f
", fabs(ans));
}

int main(){
//FileOpen();
	int Tasks;
	io >> Tasks;
	while(Tasks--){
		int m;
		io >> n >> m;
		Fill(a, 0);
		R(i,1,m){
			int u, v;
			io >> u >> v;
			++a[u][u];
			++a[v][v];
			--a[u][v];
			--a[v][u];
		}
		Gauss();
	}
	return 0;
}