hdu 1245 Saving James Bond（最短路）

題意：一個人從直徑爲15米的小島上踩着鯊魚跳離湖（好奇怪的題目），湖爲100*100的正方形。人最大的跳躍距離爲D，給出n個鯊魚的座標，求人跳出島的最小距離及在這情況下的跳躍次數。

建圖有點麻煩

#include<stdio.h>
#include<algorithm>
#include<string.h>
#include<queue>
#include<math.h>
#include<algorithm>
using namespace std;
#define INF 0x3f3f3f3f

struct Node{
	double x,y;
}node[110];
int n;
double d;

double distlen(Node a,Node b){
	return sqrt((a.x-b.x)*1.0*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)*1.0);
}

double mp[110][110];
int vis[110],pre[110];
double dist[110];

void spfa(int s,int t)
{
    for(int i=0;i<=n+1;i++)
    {
        dist[i]=INF;
        vis[i]=0;
        pre[i]=-1;
    }
    queue<int> q;
    q.push(s);
    dist[s]=0;
    vis[s]=1;
    while(!q.empty())
    {
        int c=q.front();
        q.pop();
        vis[c]=0;
        for(int i=0;i<=n+1;i++)
        {
            if(dist[i]>dist[c]+mp[c][i])
            {
                pre[i]=c;
                dist[i]=dist[c]+mp[c][i];
                if(!vis[i])   vis[i]=1,q.push(i);
            }
        }
    }
    if(dist[t]>=INF)
    {
        printf("can't be saved\n");
        return;
    }
    int c=t,step=0;
    while(c!=s)
        step++,c=pre[c];
    printf("%.2lf %d\n",dist[t],step);
    return;
}
double _len(Node a,Node b){
	return sqrt((a.x-b.x)*(a.x-b.x)*1.0+(a.y-b.y)*(a.y-b.y)*1.0);
}
int main(){
	

	while(scanf("%d%lf",&n,&d)!=EOF){
		
		if(n==0){
			if(d>=42.5)
			printf("42.50 1\n");
			else printf("can't be saved\n");
			continue;
		}
		
		for(int i=1;i<=n;i++)
		scanf("%lf%lf",&node[i].x,&node[i].y);
		node[n+1].x=node[n+1].y=50;
		node[0].x=node[0].y=0;
		
		if(d>=42.5){
			printf("42.50 1\n");
			continue;
		}
		for(int i=0;i<=n+1;i++)
		for(int j=0;j<=n+1;j++)
		mp[i][j]=(i==j?0:INF);
		
	 for(int i=0;i<=n;i++)
		for(int j=0;j<=n;j++){
			if(i==j)continue;
			double len=_len(node[i],node[j]);
			if(i==0||j==0)len-=7.5;
			if(len<=0)len=0;
			if(len<=d)mp[i][j]=len;
		}
        for(int i=0;i<=n;i++)
        {
            double c=min(50-node[i].x,50-node[i].y);
            c=min(c,min(50+node[i].x,50+node[i].y));
            if(c>d) c=INF;
            mp[i][n+1]=mp[n+1][i]=c;
        }
		spfa(0,n+1);
	} 
	return 0;
}