【HNOI2008】bzoj1007 水平可见直线_imlk组成单词

半平面交简化版。

#include<cstdio>
#include<algorithm>
#include<cmath>
using namespace std;
const int maxn=500010;
const double eps=1e-8;
int cmp(double x)
{
    if (x>=eps) return 1;
    if (fabs(x)<=eps) return 0;
    return -1;
}
struct Vector
{
    double x,y;
    Vector operator + (const Vector &v) const
    {
        return (Vector){x+v.x,y+v.y};
    }
    Vector operator - (const Vector &v) const
    {
        return (Vector){x-v.x,y-v.y};
    }
    Vector operator * (const double &k) const
    {
        return (Vector){x*k,y*k};
    }
}p[maxn];
typedef Vector Point;
double dot(Vector v,Vector u)
{
    return v.x*u.x+v.y*u.y;
}
double cross(Vector v,Vector u)
{
    return v.x*u.y-v.y*u.x;
}
struct Line
{
    Point p;
    Vector v;
    int id;
    /*double angle() const
    {
        return atan2(v.y,v.x);
    }*/
    bool operator < (const Line &l) const
    {
        return cmp(v.y-l.v.y)==-1;
    }
}a[maxn],q[maxn];
Point intersection(Line l,Line m)
{
    Vector u=l.p-m.p;
    double t=cross(m.v,u)/cross(l.v,m.v);
    return l.p+l.v*t;
}
int n,ans[maxn];
int main()
{
    //freopen("e.in","r",stdin);
    //freopen("e.out","w",stdout);
    //freopen("bzoj_1007.in","r",stdin);
    //freopen("bzoj_1007.out","w",stdout);
    int hd,tl;
    double x,y;
    scanf("%d",&n);
    for (int i=1;i<=n;i++)
    {
        scanf("%lf%lf",&x,&y);
        a[i]=(Line){(Point){0,y},(Vector){1,x},i};
    }
    sort(a+1,a+n+1);
    q[hd=tl=1]=a[1];
    for (int i=2;i<=n;i++)
    {
        while (hd<tl&&cmp(cross(a[i].v,p[tl-1]-a[i].p))<=0) tl--;
        //while (hd<tl&&cmp(cross(a[i].v,p[hd]-a[i].p))<=0) hd++;
        if (q[tl]<a[i]) q[++tl]=a[i];
        else if (cmp(cross(a[i].v,q[tl].p-a[i].p))<=0) q[tl]=a[i];
        if (hd<tl) p[tl-1]=intersection(q[tl-1],q[tl]);
    }
    //while (hd<tl-1&&cmp(cross(q[1].v,p[tl-1]-q[1].p))<=0) tl--;
    for (int i=hd;i<=tl;i++) ans[q[i].id]=1;
    for (int i=1;i<=n;i++)
        if (ans[i]) printf("%d ",i);
}
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