SP104 HIGH - Highways

题目

SP104 HIGH - Highways

做法

luogu上直接swap会CE

度数矩阵-邻接矩阵任意去掉一行\(i\)和一列\(i\)然后求解行列式，取单位矩矩阵乘积

裸的矩阵树啊

My complete code

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<string>
using namespace std;
typedef long long LL;
const int maxn=1e3+9;
const double eps=1e-7;
inline LL Read(){
	LL x(0),f=1; char c=getchar();
	while(c<'0'||c>'9'){
		if(c=='-')f=-1; c=getchar();
	}
	while(c>='0'&&c<='9')
	    x=(x<<3)+(x<<1)+c-'0',c=getchar();
	return x*f;
}
LL n,m,T;
double D[maxn][maxn];
inline void Solve(){
	--n;
	for(LL i=1;i<=n;++i){
		LL mx=i;
		for(LL j=i+1;j<=n;++j)
		    if(D[j][i]>D[mx][i])
		        mx=j;
		if(D[mx][i]<eps&&D[mx][i]>-eps){
			printf("0\n");
			return;
		}
		if(mx!=i){
			for(LL j=1;j<=n;++j){
				LL c(D[i][j]);
				D[i][j]=D[mx][j],D[mx][j]=c;
			}
		}
		for(LL j=i+1;j<=n;++j){
			double tmp=D[j][i]/D[i][i];
			for(LL k=i;k<=n;++k)
			    D[j][k]-=tmp*D[i][k];
		}
	}
	double ans=1.0;
	for(LL i=1;i<=n;++i)
	    ans*=D[i][i];
	printf("%0.f\n",ans);
}
int main(){
	T=Read();
	while(T--){
		n=Read(),m=Read();
		memset(D,0,sizeof(D));
		while(m--){
			LL u(Read()),v(Read());
			++D[u][u],++D[v][v],
			--D[u][v],--D[v][u];
		}
		Solve();
	}
	return 0;
}