poj 1113 凸包模板

#include <iostream>
#include <cstring>
#include <cstdio>
#include <math.h>
#include <cstdlib>
#include <algorithm>
using namespace std;
#define N 1050
#define PI acos(-1.0)
int n,r;
struct point
{
	int x,y;
	point(int _x=0,int _y=0)
	{
		x=_x;
		y=_y;
	}
	point operator-(point b)const
	{
		return point(x-b.x,y-b.y);
	}
}p[N],ch[N];
int cross(point a,point b)
{
	return a.x*b.y-a.y*b.x;
}
bool cmp(point a,point b)
{
	return a.x==b.x?a.y<b.y:a.x<b.x;
}
double dist(point a,point b)
{
	return sqrt((double)(a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}
int convexhull(point *p,int n,point *ch)
{
	sort(p+1,p+1+n,cmp);
	int m=0;
	for(int i=1;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-1;i>=1;--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 ()
{
	while(scanf("%d%d",&n,&r)!=EOF)
	{
		for(int i=1;i<=n;++i)
			scanf("%d%d",&p[i].x,&p[i].y);
		int  cnt=convexhull(p,n,ch);
		double res=0.0;
		for(int i=0;i<cnt-1;++i)
			res+=dist(ch[i],ch[i+1]);
		res+=dist(ch[cnt-1],ch[0]);
		res+=2*PI*r;
		printf("%.0lf\n",res);
	}
	
	return 0;
}