poj2074 Line of Sight 直线交点 区间合并

题意：求路上的最长连续能看到房子的长度

真的蠢 半天没想到下面这两张图 看了一眼题解被自己蠢哭

面向discuss编程

漏算了起始区间 末尾区间 以及初始化问题 嗯 分别wa了一次

int main()
{
//    freopen("in.txt","r",stdin);
    Line house,road;
    double x1,x2,y;
    int n,k,m;
    while(scanf("%lf%lf%lf",&x1,&x2,&y)!=EOF)
    {
        if(sgn(x1+x2+y)==0)break;
        house=Line(Point(x1,y),Point(x2,y));
        scanf("%lf%lf%lf",&x1,&x2,&y);
        road=Line(Point(x1,y),Point(x2,y));
        scanf("%d",&n);
        k=0;
        for(int i=0;i<n;i++)
        {
            scanf("%lf%lf%lf",&x1,&x2,&y);
            if(sgn((y-house.s.y)*(y-road.s.y))>=0)continue;
            ob[k++]=Line(Point(x1,y),Point(x2,y));
        }
        if(!k)
        {
            printf("%.2lf\n",road.e.x-road.s.x);
            continue;
        }
        sort(ob,ob+k);
        for(int i=0;i<k;i++)
        {
            Line t=Line(house.e,ob[i].s);
            Point st=t&road;
            t=Line(house.s,ob[i].e);
            Point et=t&road;
            broad[i]=Line(st,et);
        }
        sort(broad,broad+k);
        double ans=0;
        croad[0]=broad[0];
        if(sgn(croad[0].s.x-road.s.x)>0)ans=croad[0].s.x-road.s.x;
        m=1;
        for(int i=1;i<k;i++)
        {
            if(sgn(broad[i].s.x-croad[m-1].e.x)<0)
            {
                croad[m-1].e.x=max(croad[m-1].e.x,broad[i].e.x);
            }
            else
            {
                croad[m++]=broad[i];
            }
        }
        for(int i=1;i<m;i++)
        {
            ans=max(ans,croad[i].s.x-croad[i-1].e.x);
            if(sgn(croad[i].e.x-road.e.x)>0)break;
        }
        if(sgn(croad[m-1].e.x-road.e.x)<0)ans=max(road.e.x-croad[m-1].e.x,ans);
        if(sgn(ans)>0)
        printf("%.2lf\n",ans);
        else
            printf("No View\n");
    }
    return 0;
}