凸包模板

#include<stdio.h>
#include<algorithm>
#include<string.h>
#define N 105
using namespace std;
struct point
{
	int x,y,id;
	point(){}
	point(int x,int y)
	{
		this->x=x;
		this->y=y;
	}
}p[N],tubao[N];
point operator-(point A,point B)  
{  
    return point(A.x-B.x,A.y-B.y);  
}  
bool cmp(point a,point b)
{
	if(a.x==b.x)return a.y<b.y;
	return a.x<b.x;
}
int Cross(point A,point B)  
{  
    return A.x*B.y-A.y*B.x;  
}  
int ConvexHull(point* p,int n,point* ch)//求凸包  
{  
    int m=0;  
    for(int i=0;i<n;i++)  
    {  
        while(m>1&&Cross(ch[m-1]-ch[m-2],p[i]-ch[m-2])<=0)m--;  
        ch[m++]=p[i];  
    }  
    int k=m;  
    for(int i=n-2;i>=0;i--)  
    {  
        while(m>k&&Cross(ch[m-1]-ch[m-2],p[i]-ch[m-2])<=0)m--;  
        ch[m++]=p[i];  
    }  
    if(n>1)m--;  
    return m;  
}  
int main()
{
	int n;
	scanf("%d",&n);
	for(int i=0;i<n;i++)
		scanf("%d%d",&p[i].x,&p[i].y);
	sort(p,p+n,cmp);
	int tot=ConvexHull(p,n,tubao);
}