POJ 1113 Wall

#include<iostream>
#include<cmath>
using namespace std;
const double PI=acos(-1.0);
int n,l;
typedef struct point
{
	double x,y;
	point(double xx=0,double yy=0):x(xx),y(yy){}
}vector;
point p[1010],q[1010];
void sort1(point *a,int x,int y,point *t)
{
	int m,u,v,i;
	if(y-x>1)
	{
		m=x+(y-x)/2;
		u=x,v=m,i=x;
		sort1(a,x,m,t);
		sort1(a,m,y,t);
		while(u<m || v<y)
		{
			if(v>=y || (u<m && (a[u].x<a[v].x || (a[u].x==a[v].x && a[u].y<=a[v].y)))) t[i++]=a[u++];
			else t[i++]=a[v++];
		}
		for(i=x;i<y;i++) a[i]=t[i];
	}
}
vector operator - (point a,point b) {return vector(a.x-b.x,a.y-b.y);}
double cross(vector a,vector b)
{
	return a.x*b.y-a.y*b.x;
}
int convex(point *a,point *t)
{
	int k,m=0,i;
	for(i=0;i<n;i++)
	{
		while(m>1 && cross(t[m-1]-t[m-2],a[i]-t[m-2])<=0) m--;
		t[m++]=a[i];
	}
	k=m;
	for(i=n-1;i>=0;i--)
	{
		while(m>k && cross(t[m-1]-t[m-2],a[i]-t[m-2])<=0) m--;
		t[m++]=a[i];
	}
	if(n>1) m--;
	return m;
}
double dot(vector a,vector b)
{
	return a.x*b.x+a.y*b.y;
}
double length(vector a)
{
	return sqrt(dot(a,a));
}
int main()
{
	int i,m;
	double s;
	while(cin>>n>>l)
	{
		s=0.0;
		for(i=0;i<n;i++)
			cin>>p[i].x>>p[i].y;
		sort1(p,0,n,q);
		m=convex(p,q);
		for(i=0;i<m;i++)
		{
			s+=length(q[i]-q[(i+1)%m]);
		}
		s+=2*PI*l;
		cout<<(int)(s+0.5)<<endl;
	}
	return 0;
}