【bzoj1007】[HNOI2008]水平可见直线

#include<algorithm>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<cmath>
using namespace std;
 
#define eps 1e-8
#define N 50010
 
struct Node
{
    double a,b;
    int id;
}l[N];
 
int n;
int t=1;
 
int s[N],ans[N];
 
bool cmp(Node a,Node b)
{
    return a.a==b.a ? a.b>b.b : a.a<b.a;
}
 
double crossx(Node x1,Node x2)
{
    return (x2.b-x1.b)/(x1.a-x2.a);
}
 
int main()
{
    scanf("%d",&n);
    for (int i=1;i<=n;i++)
        scanf("%lf%lf",&l[i].a,&l[i].b),l[i].id=i;
    sort(l+1,l+n+1,cmp);
    s[1]=1;
    for (int i=2;i<=n;i++)
        if (l[i].a-l[i-1].a>=eps)
        {
            while (t>1 && crossx(l[i],l[s[t]])<=crossx(l[s[t]],l[s[t-1]]))
                t--;
            s[++t]=i;
        }
    for (int i=1;i<=t;i++)
        ans[l[s[i]].id]=1;
    for (int i=1;i<=n;i++)
        if (ans[i])
            printf("%d ",i);
    return 0;     
}