luogu P1354 房间最短路问题 计算几何_Floyd_线段交

第一次写计算几何，还是很开心的吧（虽然题目好水qaq)

暴力枚举端点，暴力连边即可

用线段交判一下是否可行.

Code:

#include <cstdio>
#include <algorithm>
#include <cmath>
#include <cstring>
#define setIO(s) freopen(s".in","r",stdin)
#define maxn 100008
const double eps = 0.00000001;
const double inf = 10000000000.0;
using namespace std;
int n,idx,ls,st,ed;
double map[200][200];
struct Point{ double x,y;  Point(double x=0,double y=0):x(x),y(y){}   }point[maxn];
struct Line{  Point a,b;  }line[maxn];
int exis(double t){ return (fabs(t)<=eps) ? 0 : (t < 0 ? -1 : 1 ) ; }
double det(double x1,double y1,double x2,double y2) { return x1*y2-x2*y1;  }
double cross(Point a,Point b,Point c) { return det(b.x-a.x,b.y-a.y,c.x-a.x,c.y-a.y);  }
bool check(Point a,Point b,Point c,Point d) {
    if((exis(cross(a,c,b)) ^ exis(cross(a,d,b)))==-2 && (exis(cross(d,a,c)) ^ exis(cross(d,b,c))) == -2)
        return true;
    return false;
}
double dis(Point a,Point b) {
    double xx = b.x - a.x;
    double yy = b.y - a.y;
    return (double)sqrt(xx*xx+yy*yy) ;
}
bool is_ok(int a,int b) {
    for(int i=1;i<=ls;++i)
    {
        if(check(line[i].a,line[i].b,point[a],point[b])) {
            return false;
        }
    }
    return true;
}
void addline(double a,double b,double c,double d)
{
    line[++ls].a.x = a;
    line[ls].a.y = b;
    line[ls].b.x = c;
    line[ls].b.y = d;
}
void addedge(int u,int v,double dis) { map[u][v] = dis;}
int main(){
    //setIO("input");
    scanf("%d",&n);
    for(int i=1;i<=n;++i) {
        double a,b,c,d,x;
        scanf("%lf%lf%lf%lf%lf",&x,&a,&b,&c,&d);
        point[++idx] = Point(x,a);
        point[++idx] = Point(x,b);
        point[++idx] = Point(x,c);
        point[++idx] = Point(x,d);
        addline(x,0,x,a);
        addline(x,b,x,c);
        addline(x,d,x,10.0);
    }
    point[++idx] = Point(0,5), st=idx;
    point[++idx] = Point(10,5),ed=idx;
    for(int i=1;i<=idx;++i)
        for(int j=1;j<=idx;++j) map[i][j] = inf;
            for(int i=1;i<=idx;++i) map[i][i]=0;
    for(int i=1;i<=idx;++i)
        for(int j=1;j<i;++j)
            if(i!=j&&is_ok(i,j))
                addedge(i,j,dis(point[i],point[j])),addedge(j,i,dis(point[i],point[j]));
    for(int k=1;k<=idx;++k)
        for(int i=1;i<=idx;++i)
            for(int j=1;j<=idx;++j)
                if(map[i][k]+map[k][j] < map[i][j]) map[i][j] = map[i][k] + map[k][j];
    printf("%.2f",map[st][ed]);
    return 0;
}