POJ 1113 凸包

凸包问题 我的一个凸包

求出凸包面积 然后加上2*PI*l

#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;
const int n_max=1005;
const double PI=acos(-1.0);
struct point
{
	double x,y;
	void init(double tx,double ty)
	{
		x=tx;
		y=ty;
	}
	void operator = (const point &p)
	{
		x=p.x;
		y=p.y;
	}
}p[n_max],ans[n_max];

bool bigger(point a,point b)
{
	if(a.y==b.y)
	{
		return a.x<b.x;
	}
	return a.y<b.y;
}

bool smaller(point a,point b)
{
	if(a.y==b.y)
	{
		return a.x>b.x;
	}
	return a.y>b.y;
}

double det(point a,point b,point c)
{
	double x1=b.x-a.x;
	double y1=b.y-a.y;
	double x2=c.x-a.x;
	double y2=c.y-a.y;
	return x1*y2-x2*y1;
}

int Graham_scan(point *p,int n,point *ans)
{
	int top=0;
	ans[top++]=p[0];
	ans[top++]=p[1];
	int i;
	for(i=2;i<n;i++)
	{
		while(top>1)
		{
			if(det(ans[top-2],ans[top-1],p[i])<0)
			{
				top--;
			}
			else
			{
				break;
			}
		}
		ans[top++]=p[i];
	}
	return top;
}

int graham_scan(point *p,int n,point *ans)
{
	sort(p,p+n,smaller);
	int t=Graham_scan(p,n,ans);
	sort(p,p+n,bigger);
	return t+Graham_scan(p,n,ans+t-1)-1;
}

double dist(point a,point b)
{
	return sqrt((a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y));
}

int main()
{
	int n,l;
	double x,y;
	while(~scanf("%d%d",&n,&l))
	{
		int i;
		for(i=0;i<n;i++)
		{
			scanf("%lf%lf",&x,&y);
			p[i].init(x,y);
		}
		int nans=graham_scan(p,n,ans);
		double sum=0;
		for(i=1;i<nans;i++)
		{
			sum+=dist(ans[i],ans[i-1]);
		}
		sum+=2*l*PI;
		printf("%d\n",(int)(sum+0.5));
	}
	return 0;
}