poj 1556 The Doors(最短路+几何)

题意：有一个小屋，起点在(0,5)，重点在(10,5)，中间有0—18堵墙，每堵墙上有两个门，求起点到终点最短路

思路：起点和终点和门的端点建图求最短路，在求两个端点之间的距离（直线距离）的时候要判断两个端点之间是否有墙隔着

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iomanip>
#include <cmath>
using namespace std;

const int MAXN = 150;
const double INF = 9999999;
const double precision = 1e-8;
struct Point
{
double x,y;
Point(){}
Point(double xx, double yy):x(xx),y(yy){}
};
struct Line
{
Point sp,ep;
Line(){}
Line(Point a, Point b):sp(a),ep(b){}
};
int n,pcnt,lcnt;
Point ps[MAXN];
Line ls[MAXN];
double g[MAXN][MAXN];
double dis[MAXN];
int book[MAXN];

double dist(Point a, Point b)
{
return sqrt((a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y));
}

int dblcmp(double d)
{
if(fabs(d) < precision)
return 0;
return d > 0 ? 1 : -1;
}

double det(Point a, Point b, Point c)
{
//b.x-a.x,b.y-a.y
//c.x-a.x,c.y-a.y
return (b.x-a.x)*(c.y-a.y) - (c.x-a.x)*(b.y-a.y);
}

bool intersect(Point a, Point b, Line p)
{
int d1 = dblcmp(det(a,b,p.sp));
int d2 = dblcmp(det(a,b,p.ep));
int d3 = dblcmp(det(p.sp,p.ep,a));
int d4 = dblcmp(det(p.sp,p.ep,b));
if(d1*d2 < 0 && d3*d4 < 0)
return true;
return false;
}

bool check(int i, int j)
{
for(int k = 0; k < lcnt; ++k)
{
if(intersect(ps[i],ps[j],ls[k]))
return false;
}
return true;
}

double dijkstra()
{
memset(book,0,sizeof(book));
for(int i = 1; i <= pcnt; ++i)
dis[i] = g[1][i];
book[1] = 1;
double minn;
int u,v;
for(int i = 1; i <= pcnt-1; ++i)
{
minn = INF;
for(int j = 1; j <= pcnt; ++j)
{
if(book[j] == 0 &&  dis[j] < minn)
{
minn = dis[j];
u = j;
}
}
book[u] = 1;
for(v = 1; v <= pcnt; ++v)
{
if(dis[v] > dis[u] + g[u][v])
dis[v] = dis[u] + g[u][v];
}
}
return dis[pcnt];
}

int main()
{
double x,y;
while(scanf("%d",&n) && n != -1)
{
pcnt = 1;
lcnt = 0;
memset(g,0,sizeof(g));
ps[pcnt++] = Point(0,5);
for(int i = 0; i < n; ++i)
{
cin >> x;
for(int k = 0; k < 4; ++k)
{
cin >> y;
ps[pcnt++] = Point(x,y);
}
ls[lcnt++] = Line(Point(x,0),ps[pcnt-4]);
ls[lcnt++] = Line(ps[pcnt-3],ps[pcnt-2]);
ls[lcnt++] = Line(ps[pcnt-1],Point(x,10));
}
ps[pcnt] = Point(10,5);
for(int i = 1; i <= pcnt; ++i)
{
for(int j = 1; j <= pcnt; ++j)
{
if(i == j) g[i][j] = 0;
else if(check(i,j)) g[i][j] = dist(ps[i],ps[j]);
else g[i][j] = INF;
}
}
double res = dijkstra();
//        for(int k = 1; k <= pcnt; ++k)
//        {
//            for(int i = 1; i <= pcnt; ++i)
//            {
//                for(int j = 1; j <= pcnt; ++j)
//                    if(g[i][k]+g[k][j] < g[i][j])
//                        g[i][j] = g[i][k] + g[k][j];
//            }
//        }
cout << fixed << setprecision(2) << res << endl;
}
return 0;
}