poj 2253 Frogger

#include<map>
#include<set>
#include<stack>
#include<queue>
#include<cmath>
#include<vector>
#include<cstdio>
#include<string>
#include<cstring>
#include<cstdlib>
#include<iostream>
#include<algorithm>
#define  inf 0x0f0f0f0f
using namespace std;

const int MAX=200+10;
const double esp=1e-8;

typedef pair<int,int>pii;
priority_queue<pii,vector<pii>,greater<pii> >q;

struct node
{
    int id,cost;
};
vector<node> stone[MAX];

int dist[MAX],n;
bool vis[MAX];
double dis[MAX][MAX],xx[MAX],yy[MAX];

void dijkstra(int k)
{
    for(int i=0;i<=n;i++) dist[i]=(i==k? 0 : 99999999);
    memset(vis,0,sizeof(vis));

    q.push(make_pair(dist[k],k));
    while(!q.empty())
    {
        pii u=q.top();
        q.pop();
        int x=u.second;
        if(!vis[x])
        {
            vis[x]=true;
            for (int i=0;i<stone[x].size();i++)
            {
                if(dist[stone[x][i].id]>dist[x]+stone[x][i].cost)
                {
                    dist[stone[x][i].id]=dist[x]+stone[x][i].cost;
                    q.push(make_pair(dist[stone[x][i].id],stone[x][i].id));
                }
            }
        }
    }
}

void get_dist()
{
    for (int i=1;i<=n;i++)
    for (int j=1;j<=n;j++)
    {
        dis[i][j]=sqrt((xx[i]-xx[j])*(xx[i]-xx[j])+(yy[i]-yy[j])*(yy[i]-yy[j]));
    }
}

void update(double st)
{
    for (int i=0;i<=n;i++) stone[i].clear();
    for (int i=1;i<=n;i++)
    for (int j=1;j<=n;j++)
    {
        if(dis[i][j]-st>esp)
        {
            node temp;
            temp.id=j; temp.cost=1;
            stone[i].push_back(temp);
            temp.id=i;
            stone[j].push_back(temp);
        }
        else
        {
            node temp;
            temp.id=j; temp.cost=0;
            stone[i].push_back(temp);
            temp.id=i;
            stone[j].push_back(temp);
        }
    }
}

double find(double x,double y)
{
    while (y-x>esp)
    {
        double m=x+(y-x)/2;
        update(m);
        dijkstra(1);
        if (dist[2]==0) y=m;
        else x=m;
    }
    return x;
}

int main()
{
    int caset=0;
    while (scanf("%d",&n)!=EOF && n)
    {
        caset++;
        for (int i=1;i<=n;i++)
        {
            scanf("%lf%lf",&xx[i],&yy[i]);
        }
        get_dist();
        double ans=find(0,dis[1][2]);
        printf("Scenario #%d\n",caset);
        printf("Frog Distance = %.3lf\n\n",ans);
    }
    return 0;
}