SPOJ HIGH Highways(生成树计数模板题)
题目链接：https://www.spoj.com/problems/HIGH/en/
题意是有n个城市，要修m条高速公路，使这n个城市连通，问共有多少种方案。
这道题就是求无向图的最小生成树的个数，所以直接用生成树计数(不取模的模板就好了)...不知道为啥现在贴的呆码显示出来的缩进都是乱的，凑合着看吧...
AC代码：
#include <bits/stdc++.h>
#define ll long long
#define maxn 55
#define inf 0x3f3f3f3f
using namespace std;
ll A[maxn][maxn];
ll B[maxn][maxn];
int n, m, k;
ll det(){
ll res = 1;
for (int i=1;i<=n;i++){
for (int j=i+1;j<=n;j++){
while (B[j][i]){
ll t = B[i][i] / B[j][i];
for (int k=i;k<=n;k++) B[i][k] -= B[j][k] * t;
for (int k=i;k<=n;k++) swap(B[i][k], B[j][k]);
res = -res;
}
}
if (B[i][i] == 0) return 0;
res = res * B[i][i];
}
if(res < 0) res = -res;
return res;
}
int main()
{
int T;
scanf("%d",&T);
while(T--){
scanf("%d%d",&n,&m);
memset(A, 0, sizeof(A));
memset(B, 0, sizeof(B));
for(int i=0;i<m;i++){
int u, v;
scanf("%d%d",&u,&v);
A[u][v] = A[v][u] = 1;
}
for(int i=1;i<=n;i++){
for(int j=i+1;j<=n;j++){
if(A[i][j] == 1){
B[i][i] ++;
B[i][j] = -1;
B[j][j] ++;
B[j][i] = -1;
}
}
}
n --;
ll ans = det();
printf("%lld\n", ans);
}
return 0;
}
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