spoj 104 Highways (最小生成树计数)

题目链接：http://www.spoj.pl/problems/HIGH/

题意：求最小生成树个数。

 #include<algorithm>
 #include<cstdio>
 #include<cmath>
 #include<cstring>
 #include<iostream>
 #define ll long long
 double a[][];
 int n,m;
 const double eps=1e-;
 int zero(double x){
     if (x<-eps) return -;
     else return x>eps;
 }
 double work(){
     double res=;
     for (int i=;i<=n;i++){
         int k=i;
         for (int j=i+;j<=n;j++) if (fabs(a[j][i])>fabs(a[k][i])) k=j;
         if (k!=i){
             for (int j=;j<=n;j++)
              std::swap(a[k][j],a[i][j]);
         }
         for (int j=i+;j<=n;j++){
             double tmp=a[j][i]/a[i][i];
             for (int k=i;k<=n;k++)
              a[j][k]-=tmp*a[i][k];
         }
         if (!zero(a[i][i])) return ;
     }
     for (int i=;i<=n;i++) res*=a[i][i];
     return std::fabs(res);
 }
 int main(){
     int T;
     scanf("%d",&T);
     while (T--){
         scanf("%d%d",&n,&m);
         for (int i=;i<=n;i++)
          for (int j=;j<=n;j++)
           a[i][j]=;
         while (m--){
             int x,y;
             scanf("%d%d",&x,&y);
             a[x][x]+=1.0;a[y][y]+=1.0;
             a[x][y]-=1.0;a[y][x]-=1.0;
         }
         n--;
         printf("%0.0lf\n",work());
     }
 }