http://poj.org/problem?id=3164
裸最小树形图,套模板就可以。
#include
#include
#include
#include
#include
using namespace std;
#define maxn 107
#define memset(a,b) memset(a,b,sizeof(a))
const int INF = 0x3f3f3f3f;
int pre[maxn],id[maxn],vis[maxn];
double in[maxn];
struct {
int x,y;
}p[maxn];
struct {
int u,v;
double w;
}edge[maxn*maxn];
double dis(int a, int b) {
double x = p[a].x - p[b].x, y = p[a].y - p[b].y;
return sqrt(x*x+y*y);
}
double directed_MST(int root, int n, int m) {
double ans = 0;
while(true) {
//1.找最小入边
for (int i = 0; i < n; i++) in[i] = INF;
for (int i = 0; i < m; i++) {
int u = edge[i].u, v = edge[i].v;
if (edge[i].w < in[v] && u != v) {
pre[v] = u;
in[v] = edge[i].w;
}
}
for (int i =0; i < n; i++)
if (in[i] == INF && i != root)
return -1;
//2.找环
int cnt = 0;
memset(id, -1);
memset(vis, -1);
in[root] = 0;
for (int i = 0; i < n; i++) {
ans += in[i];
int v = i;
while (vis[v] != i && id[v] == -1) {//缩点
vis[v] = i;
v = pre[v];
}
if (v != root && id[v] == -1) {
for (int u = pre[v]; u != v; u = pre[u]) id[u] = cnt;
id[v] = cnt++;
}
}
if(cnt == 0) break;
for(int i=0 ; iif(id[i] == -1) id[i] = cnt++;
//3.建立新图
for(int i=0 ; iint u = edge[i].u, v = edge[i].v;
edge[i].u = id[u];
edge[i].v = id[v];
if(id[u] != id[v]) edge[i].w -= in[v];
}
n = cnt;
root = id[root];
}
return ans;
}
int main() {
#ifndef ONLINE_JUDGE
freopen("/home/lucienshui/Desktop/in","r",stdin);
#endif
int n,m;
while(~scanf("%d%d",&n,&m)) {
for(int i=0 ; iscanf("%d%d",&p[i].x,&p[i].y);
for(int i=0 ; iscanf("%d%d",&edge[i].u,&edge[i].v);
if(--edge[i].u!=--edge[i].v) edge[i].w = dis(edge[i].u,edge[i].v);
else edge[i].w = INF;
}
double ans = directed_MST(0,n,m);
if(ans == -1) printf("poor snoopy\n");
else printf("%.2f\n",ans);
}
return 0;
}