智捅马蜂窝 RQNOJ 86

#include<cstdio>
#include<queue>
#include<cmath>
#include<cstring>
using namespace std;
int v,n;
const double INF = 10000000.00;
struct edge{
int to;
double t;
edge* next;
};
edge* head[101];
int x[101],y[101];
double d[101];
double dis(int i,int j){
	int dx = x[i]-x[j],dy = y[i] - y[j];
	return sqrt(dx * dx + dy * dy);
}
double g(int i,int j){
	return sqrt((y[j]-y[i])*2/10.0);
}
void adde(int s,int e,double w)
{
	edge* ne = new edge();
	ne->t = w;
	ne->to = e;
	ne->next = head[s];
	head[s] = ne;
}
void dij()
{
	typedef pair<double,int>pii;
	priority_queue< pii,vector<pii>,greater<pii> >q;
	q.push(make_pair(d[1],1));
	while(!q.empty())
	{
		pii u = q.top();q.pop();
		int k = u.second;
		if(d[k]!=u.first) continue;
		for(edge* i = head[k];i != NULL;i = i->next)
		{
			int p = i->to;
			if(d[p] > d[k]+(i->t))
			{
				d[p]=d[k]+(i->t);
				q.push(make_pair(d[p],p));
			}
		}
	}
}
int main()
{
	scanf("%d%d",&n,&v);
	int f;
	for(int i = 1;i <= n;++i)
	{
		scanf("%d%d%d",&x[i],&y[i],&f);
		if(f)
		{
			adde(f,i,dis(i,f)/v);
			adde(i,f,dis(i,f)/v);
		}
		d[i] = INF;
	}
	d[1] = 0;
	for(int i = 1;i <= n;++i)
	{
		for(int j = 1;j <= n;++j)
		if(x[i]==x[j] && y[i] < y[j]){
		adde(j,i,g(i,j));
		}
	}
	dij();
	printf("%.2lf",d[n]);
	return 0;
}