POJ-3164 Command Network 最小树形图 朱刘算法

#include<stdio.h>
#include<string.h>
#include<vector>
#include<math.h>
using namespace std;
const int maxn = 115;
#define type double
const type inf = 1<<30;
int n,m;
struct point
{
double x,y;
}p[maxn];
struct node
{
int u,v;
type w;
}E[maxn*maxn];
int pre[maxn],id[maxn],vis[maxn];//id为缩点后的点
type in[maxn];					//in[i]点i的最小入边权
double getdis(point a,point b)
{
return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}
type Directed_MST(int root,int nv,int ne) {
type ret = 0;
while( true ) {
//1.找最小入边
for(int i = 0; i < nv; i ++ ) in[i] = inf;
for(int i = 0; i < ne; i++){
int u = E[i].u;
int v = E[i].v;
if(E[i].w < in[v] && u != v) {
pre[v] = u;
in[v] = E[i].w;
}
}
for( int i = 0; i < nv; i ++ ) {
if( i == root ) continue;
if( in[i] == inf )    return -1;//除了跟以外有点没有入边,则根无法到达它
}
//2.找环
int cntnode = 0;
memset(id,-1,sizeof(id));
memset(vis,-1,sizeof(vis));
in[root] = 0;
for(int i = 0; i < nv; i ++ ) {//标记每个环
ret += in[i];
int v = i;
while( vis[v] != i && id[v] == -1 && v != root) {
vis[v] = i;
v = pre[v];
}
if( v != root && id[v] == -1) {
for( int u = pre[v] ; u != v ; u = pre[u]) {
id[u] = cntnode;
}
id[v] = cntnode ++;
}
}
if( cntnode == 0 )    break;//无环
for( int i = 0; i < nv; i ++ )
if( id[i] == -1 ) {
id[i] = cntnode ++;
}
//3.缩点,重新标记
for( int i = 0; i < ne; i ++) {
int v = E[i].v;           //注意 E[i].v 下面改变了
E[i].u = id[E[i].u];
E[i].v = id[E[i].v];
if(E[i].u != E[i].v) {
E[i].w -= in[v];      //这里的v不能直接用E[i].v
}
}
nv = cntnode;
root = id[root];
}
return ret;
}
int main()
{
//freopen("data.txt","r",stdin);
while( scanf("%d%d",&n,&m) != EOF ){
for( int i = 0; i < n; i ++ )
scanf("%lf%lf",&p[i].x,&p[i].y);
for( int i = 0; i < m; i ++ ){
scanf("%d%d",&E[i].u,&E[i].v);
E[i].u --;	E[i].v --;
if( E[i].u != E[i].v )
E[i].w = getdis(p[E[i].u],p[E[i].v]);
else
E[i].w = inf;
}
type ans = Directed_MST(0,n,m);
if( ans == -1 )
printf("poor snoopy\n");
else
printf("%.2f\n",ans);
}
return 0;
}