Wall

 1 #include<cstdio>
 2 #include<iostream>
 3 #include<cmath>
 4 #include<algorithm>
 5 #define Max 1005
 6 using namespace std;
 7 const double pi=acos(-1.0);
 8 int n,l,top;//top记录栈顶
 9 double ans; 
10 struct point{
11     double x,y;
12     point(double X=0,double Y=0){x=X,y=Y;}
13     friend bool operator <(point a,point b){
14         return a.x<b.x||(a.x==b.x&&a.y<b.y);//xy排序 
15     }
16 }p[Max],que[Max];//que保存凸包节点 栈
17 point operator +(point a,point b){return point(a.x+b.x,a.y+b.y);}
18 point operator -(point a,point b){return point(a.x-b.x,a.y-b.y);}
19 double cross(point a,point b){return a.x*b.y-a.y*b.x;} //若<=0 说明b在a的顺时针方向 
20 double len(point a){return sqrt(a.x*a.x+a.y*a.y);}
21 int main()
22 {
23     scanf("%d%d",&n,&l);
24     for(int i=1;i<=n;i++)scanf("%lf%lf",&p[i].x,&p[i].y);
25     sort(p+1,p+n+1);
26     for(int i=1;i<=n;i++){//下凸壳 
27         while(top>1&&cross(que[top]-que[top-1],p[i]-que[top-1])<=0)top--;
28         que[++top]=p[i];
29     }
30     int tmp=top;
31     for(int i=n-1;i>=1;i--){//上凸壳 
32         while(top>tmp&&cross(que[top]-que[top-1],p[i]-que[top-1])<=0)top--;
33         que[++top]=p[i];
34     }
35     for(int i=1;i<=top;i++) ans+=len(que[i%top+1]-que[(i+1)%top+1]);
36     ans+=2*pi*l;
37     printf("%.0lf",ans);
38     return 0;
39 }