BZOJ 1007 [HNOI2008]水平可见直线 ——计算几何

用了trinkle的方法，半平面交转凸包。

写了一发，既没有精度误差，也很好写。

#include <map>
#include <ctime>
#include <cmath>
#include <queue>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
#define F(i,j,k) for (int i=j;i<=k;++i)
#define D(i,j,k) for (int i=j;i>=k;--i)
#define ll long long

struct Vector{
int x,y;
void print()
{
printf("Vector - > (%d,%d)\n",x,y);
}
};

struct Point{
int x,y;
int id;
void print()
{
printf("Point ID %d (%d,%d)\n",id,x,y);
}
};

Vector operator - (Point a,Point b)
{Vector ret;ret.x=a.x-b.x;ret.y=a.y-b.y;return ret;}

ll operator * (Vector a,Vector b)
{return (ll)a.x*b.y-(ll)a.y*b.x;}

int n,top=0;
Point a[50005],sta[50005];

bool cmp(Point a,Point b)
{return a.x==b.x?a.y<b.y:a.x<b.x;}
bool cmp2(Point a,Point b)
{return a.id<b.id;}
void Andrew()
{
F(i,1,n)
if (a[i].x!=a[i-1].x){
while (top>=2&&(sta[top]-sta[top-1])*(a[i]-sta[top])<=0) top--;
sta[++top]=a[i];
}
sort(sta+1,sta+top+1,cmp2);
F(i,1,top) printf("%d ",sta[i].id);
printf("\n");
}

void Finout()
{
freopen("bzoj_1007.in","r",stdin);
freopen("bzoj_1007.out","w",stdout);
}

int main()
{
//  Finout();
scanf("%d",&n);
F(i,1,n)
{
scanf("%d%d",&a[i].x,&a[i].y);
a[i].y=-a[i].y;
a[i].id=i;
}
sort(a+1,a+n+1,cmp);
Andrew();
}