【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
;

int n;
int t=1;

int s
,ans
;

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;
}