spoj HIGH - Highways

題目鏈接

題意：生成樹計數模版題

#include<stdio.h>
#include<iostream>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<string.h>
#include<queue>
#include<stack>
#include<list>
#include<map>
#include<set>
#include<vector>
using namespace std;
typedef long long int ll;
const int maxn =110;
const int maxm=10000;
const int mod =1e8+7;
const int INF=0x3f3f3f3f;
const double eps=1e-8;
int sgn(double x)
{
	if(fabs(x)<eps)return 0;
	if(x<0)return -1;
	else return -1;
}
double b[maxn][maxn];
double det(double a[][maxn],int n)
{
	int i,j,k;
	int sign=0;
	double ret=1;
	for( i=0;i<n;i++)
		for( j=0;j<n;j++)
			b[i][j]=a[i][j];
	for( i=0;i<n;i++)
	{
		if(sgn(b[i][i])==0)
		{
			for( j=i+1;j<n;j++)
				if(sgn(b[i][j])!=0)
					break;
			if(j==n)return 0;
			for( k=i;k<n;k++)
				swap(b[i][k],b[j][k]);
			sign++;
		}
		ret*=b[i][i];
		for( k=i+1;k<n;k++)
			b[i][k]/=b[i][i];
		for( j=i+1;j<n;j++)
			for( k=i+1;k<n;k++)
				b[j][k]-=b[j][i]*b[i][k];
	}
	if(sign&1)ret=-ret;
	return ret;
}
double a[maxn][maxn];
int g[maxn][maxn];
int main()
{
	int t;scanf("%d",&t);
	while(t--)
	{
		int n,m;scanf("%d%d",&n,&m);
		memset(g,0,sizeof(g));
		while(m--)
		{
			int u,v;
			scanf("%d%d",&u,&v);
			u--,v--;
			g[u][v]=g[v][u]=1;
		}
		memset(a,0,sizeof(a));
		for(int i=0;i<n;i++)
			for(int j=0;j<n;j++)
				if(i!=j&&g[i][j])
				{
					a[i][i]++;
					a[i][j]=-1;
				}
		double ans=det(a,n-1);
		printf("%.0lf\n",ans);
	}
	return 0;
}