P3829 [SHOI2012]信用卡凸包

题意

通过观察发现答案为一个整圆+所有除去圆弧的四个顶点形成的凸包的周长，于是直接套模板就好了。

code:

#include
using namespace std;
const int maxn=10010;
const double eps=1e-8;
const double Pi=acos(-1.0);
int n,tot,top;
int sta[maxn];
double H,L,R,ans;
struct Point{
    double x,y;
    Point operator+(const Point& a)const{return (Point){x+a.x,y+a.y};}
    Point operator-(const Point& a)const{return (Point){x-a.x,y-a.y};}
    Point operator*(const double& k){return (Point){x*k,y*k};}
    Point operator/(const double& k){return (Point){x/k,y/k};}
    double operator*(const Point& a)const{return x*a.y-y*a.x;}
    double operator&(const Point& a)const{return x*a.x+y*a.y;}
}p[maxn<<2];
inline int dcmp(double x)
{
    if(fabs(x)<=eps)return 0;
    return x<0?-1:1;
}
inline Point turn(Point a,double theta){return (Point){a.x*cos(theta)-a.y*sin(theta),a.x*sin(theta)+a.y*cos(theta)};}
inline double dis(double x1,double y1,double x2,double y2){return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));}
inline bool cmp(Point a,Point b){return a.x==b.x?a.y1&&dcmp((p[sta[top]]-p[sta[top-1]])*(p[i]-p[sta[top]]))<=0)top--;
        sta[++top]=i;
    }
    int tmp=top;
    for(int i=tot-1;i;i--)
    {
        while(top>tmp&&dcmp((p[sta[top]]-p[sta[top-1]])*(p[i]-p[sta[top]]))<=0)top--;
        sta[++top]=i;
    }
    for(int i=1;i