poj2502 Subway

思路：

需要注意的地方：一条地铁线路并不一定和样例描述的那样是直的；同一条线路上的两个站点步行可能更快。

实现：

 #include <iostream>
 #include <cstdio>
 #include <cmath>
 using namespace std;
 
 const int MAXN = , INF = 0x3f3f3f3f;
 int sx, sy, ex, ey;
 double dis[MAXN][MAXN];
 
 struct node
 {
     int x, y;
 };
 node a[MAXN];
 
 int square(int x)
 {
     return x * x;
 }
 
 double cal(int i, int j)
 {
     return sqrt((double)square(a[i].x - a[j].x) + (double)square(a[i].y - a[j].y));
 }
 
 int main()
 {
     int x, y;
     cin >> sx >> sy >> ex >> ey;
     a[].x = sx; a[].y = sy;
     int tmp = , cnt = ;
     for (int i = ; i < MAXN; i++)
     {
         for (int j = ; j < MAXN; j++)
         {
             dis[i][j] = INF;
         }
     }
     for (int i = ; i < MAXN; i++) dis[i][i] = ;
     while (cin >> x >> y)
     {
         if (x == - && y == -)
         {
             for (int i = tmp; i < cnt - ; i++)
                 dis[i][i + ] = dis[i + ][i] = cal(i, i + ) / 40.0;
             tmp = cnt;
             continue;
         }
         a[cnt++].x = x; a[cnt - ].y = y;
     }
     a[cnt].x = ex; a[cnt].y = ey;
     for (int i = ; i <= cnt; i++)
     {
         for (int j = i + ; j <= cnt; j++)
         {
             dis[i][j] = dis[j][i] = min(dis[i][j], cal(i, j) / 10.0);
         }
     }
     for (int k = ; k <= cnt; k++)
     {
         for (int i = ; i <= cnt; i++)
         {
             for (int j = ; j <= cnt; j++)
                 if (dis[i][k] + dis[k][j] < dis[i][j])
                     dis[i][j] = dis[i][k] + dis[k][j];
         }
     }
 
     cout << int(dis[][cnt] / 1000.0 * 60.0 + 0.5) << endl;
     return ;
 }