spoj 106 Highways (最小生成树计数)

Posted 2020-07-14 GFY

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

题意：求最小生成树个数。

 1 #include<algorithm>
 2 #include<cstdio>
 3 #include<cmath>
 4 #include<cstring>
 5 #include<iostream>
 6 #define ll long long
 7 double a[205][205];
 8 int n,m;
 9 const double eps=1e-15;
10 int zero(double x){
11     if (x<-eps) return -1;
12     else return x>eps;
13 }
14 double work(){
15     double res=1;
16     for (int i=1;i<=n;i++){
17         int k=i;
18         for (int j=i+1;j<=n;j++) if (fabs(a[j][i])>fabs(a[k][i])) k=j;
19         if (k!=i){
20             for (int j=1;j<=n;j++)
21              std::swap(a[k][j],a[i][j]);
22         }
23         for (int j=i+1;j<=n;j++){
24             double tmp=a[j][i]/a[i][i];
25             for (int k=i;k<=n;k++)
26              a[j][k]-=tmp*a[i][k];
27         }
28         if (!zero(a[i][i])) return 0;
29     }
30     for (int i=1;i<=n;i++) res*=a[i][i];
31     return std::fabs(res);
32 }
33 int main(){
34     int T;
35     scanf("%d",&T);
36     while (T--){
37         scanf("%d%d",&n,&m);
38         for (int i=0;i<=n;i++)
39          for (int j=0;j<=n;j++)
40           a[i][j]=0;
41         while (m--){
42             int x,y;
43             scanf("%d%d",&x,&y);
44             a[x][x]+=1.0;a[y][y]+=1.0;
45             a[x][y]-=1.0;a[y][x]-=1.0;
46         }  
47         n--;
48         printf("%0.0lf\n",work());
49     }
50 }