poj2502 最短路

  1 //Accepted    504 KB    16 ms
  2 //spfa最短路
  3 //把n个地铁站作为n个顶点，边权为从一个站到另一个站的时间
  4 //注意：地铁在相邻的两站之间是直线行驶，但其他的就不是了
  5 #include <cstdio>
  6 #include <cstring>
  7 #include <iostream>
  8 #include <queue>
  9 #include <cmath>
 10 #include <algorithm>
 11 using namespace std;
 12 /**
 13   * This is a documentation comment block
 14   * 如果有一天你坚持不下去了，就想想你为什么走到这儿！
 15   * @authr songt
 16   */
 17 const int imax_n = 205;
 18 const double inf = 1000000000000000000.0;
 19 double x[imax_n];
 20 double y[imax_n];
 21 double a[imax_n][imax_n];
 22 double dis[imax_n];
 23 bool vis[imax_n];
 24 int n;
 25 double getDis(double x1,double y1,double x2,double y2)
 26 {
 27     return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
 28 }
 29 void init()
 30 {
 31     for (int i=1;i<=n;i++)
 32     {
 33         for (int j=1;j<=n;j++)
 34         {
 35             if (fabs(a[i][j])<1e-9)
 36             {
 37                 a[i][j]=getDis(x[i],y[i],x[j],y[j])*3.0/500;
 38                 //printf("%d %d ==> %d %d\n",x[i],y[i],x[j],y[j]);
 39             }
 40         }
 41     }
 42 }
 43 bool relax(int u,int v,double c)
 44 {
 45     if (dis[v]-dis[u]-c>1e-9)
 46     {
 47         dis[v]=dis[u]+c;
 48         return true;
 49     }
 50     return false;
 51 }
 52 queue<int > q;
 53 bool spfa(int src)
 54 {
 55     while (!q.empty()) q.pop();
 56     for (int i=1;i<=n;i++)
 57     dis[i]=inf;
 58     dis[src]=0;
 59     memset(vis,0,sizeof(vis));
 60     q.push(src);
 61     vis[src]=true;
 62     while (!q.empty())
 63     {
 64         int pre=q.front();
 65         q.pop();
 66         vis[pre]=false;
 67         for (int i=1;i<=n;i++)
 68         if (relax(pre,i,a[pre][i]) && !vis[i])
 69         {
 70             vis[i]=true;
 71             q.push(i);
 72         }
 73     }
 74 }
 75 int main()
 76 {
 77     scanf("%lf%lf%lf%lf",&x[1],&y[1],&x[2],&y[2]);
 78     n=2;
 79     double ca,cb;
 80     int start,end;
 81     int flag=0;
 82     for (int i=1;i<imax_n;i++)
 83     {
 84         for (int j=1;j<imax_n;j++)
 85         a[i][j]=0.0;
 86     }
 87     while (scanf("%lf%lf",&ca,&cb)!=EOF)
 88     {
 89         if (ca==-1 && cb==-1)
 90         {
 91             end=n;
 92             for (int i=start;i<end;i++)
 93             {
 94                     a[i][i+1]=a[i+1][i]=getDis(x[i],y[i],x[i+1],y[i+1])*3.0/2000;
 95                     //printf("%d %d ==> %d %d\n",x[i],y[i],x[j],y[j]);
 96             }
 97             flag=0;
 98             continue;
 99         }
100         ++n;
101         x[n]=ca;
102         y[n]=cb;
103         if (flag==0)
104         {
105             start=n;
106             flag=1;
107         }
108     }
109     init();
110     spfa(1);
111     printf("%.0f\n",dis[2]);
112     return 0;
113 }