【计算几何】【凸包】bzoj2829 信用卡凸包

#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;
#define N 100001
#define EPS 0.00000001
typedef double db;
const db PI=acos(-1.0);
struct Point{db x,y;}p[N<<2],bao[N<<2];
bool operator < (Point a,Point b){return fabs(a.x-b.x)>=EPS?a.x<b.x:a.y<b.y;}
typedef Point Vector;
Vector operator + (Vector a,Vector b){return (Vector){a.x+b.x,a.y+b.y};}
Vector operator - (Vector a,Vector b){return (Vector){a.x-b.x,a.y-b.y};}
Vector Rotate(Vector a,db rad)
{return (Vector){a.x*cos(rad)-a.y*sin(rad),a.x*sin(rad)+a.y*cos(rad)};}
db sqr(db x){return x*x;}
db Cross(Vector a,Vector b){return a.x*b.y-a.y*b.x;}
db dist(Point a,Point b){return sqrt(sqr(a.x-b.x)+sqr(a.y-b.y));}
int n,m,en;
db a,b,r,mx,my,jiao,ans;
int main()
{
	scanf("%d%lf%lf%lf",&n,&b,&a,&r);
	a-=(2.0*r);
	b-=(2.0*r);
	for(int i=1;i<=n;++i)
	  {
	  	scanf("%lf%lf%lf",&mx,&my,&jiao);
	  	p[++m]=Rotate((Vector){a*0.5,b*0.5},jiao)+(Point){mx,my};
	  	p[++m]=Rotate((Vector){(-a)*0.5,b*0.5},jiao)+(Point){mx,my};
	  	p[++m]=Rotate((Vector){a*0.5,(-b)*0.5},jiao)+(Point){mx,my};
	  	p[++m]=Rotate((Vector){(-a)*0.5,(-b)*0.5},jiao)+(Point){mx,my};
	  }
	sort(p+1,p+1+m);
	for(int i=1;i<=m;++i)
	  {
	  	while(en>1&&Cross(bao[en]-bao[en-1],p[i]-bao[en])<=0.0)
	  	  --en;
	  	bao[++en]=p[i];
	  }
	int t=en;
	for(int i=m-1;i;--i)
	  {
	  	while(en>t&&Cross(bao[en]-bao[en-1],p[i]-bao[en])<=0.0)
	  	  --en;
	  	bao[++en]=p[i];
	  }
	for(int i=2;i<=en;++i)
	  ans+=dist(bao[i-1],bao[i]);
	printf("%.2f\n",ans+dist(bao[en],bao[1])+PI*r*2.0);
	return 0;
}