[HNOI2008]水平可见直线 半平面交

求向直线们的俯视视角中可见的直线，以为是选最大最小斜率然后往中间放。。其实就是半平面交

//#include<bits/stdc++.h>  
//#pragma comment(linker, "/STACK:1024000000,1024000000")   
#include<stdio.h>  
#include<algorithm>  
#include<queue>  
#include<string.h>  
#include<iostream>  
#include<math.h>  
#include<set>  
#include<map>  
#include<vector>  
#include<iomanip>  
using namespace std;  
#define ll long long  
#define pb push_back  
#define FOR(a) for(int i=1;i<=a;i++)  
  
const int maxn=5e4+7;    
const double eps=1e-6;

struct Line{
	double a,b;int id;
}l[maxn];

bool cmp(Line l1,Line l2){
	if(fabs(l1.a-l2.a)<eps)return l1.b<l2.b;
	return l1.a<l2.a;
}

Line st[maxn];bool ans[maxn];
int top,n;

double crossx(Line l1,Line l2){	//解出l1,l2交点横坐标
	return (l2.b-l1.b)/(l1.a-l2.a);
}

void insert(Line a){
	while(top){
		if(fabs(st[top].a-a.a)<eps)top--;	//保留较高直线
		else if(top>1 && crossx(a,st[top-1])<=crossx(st[top],st[top-1]))
			top--;
		else break;
	}
	st[++top]=a;
}

void work(){
	for(int i=1;i<=n;i++)insert(l[i]);
	for(int i=1;i<=top;i++)ans[st[i].id]=1;
	for(int i=1;i<=n;i++)
		if(ans[i])printf("%d ",i);
}

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);
	work();
}