BZOJ 1113 Wall ——计算几何

凸包第一题。

自己认为自己写的是Andrew

其实就是xjb写出来居然过掉了测试。

刚开始把pi定义成了int，调了半天

#include <map>
#include <cmath>
#include <queue>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
#define F(i,j,k) for (int i=j;i<=k;++i)
#define D(i,j,k) for (int i=j;i>=k;--i)
#define eps 1e-10
#define ll long long
#define mp make_pair

const double pi=acos(-1.0);

struct Vector{
	double x,y;
	void print()
	{
		printf("Vector - > (%.3f,%.3f)\n",x,y);
	}
};
struct Point{
	double x,y;
	void print()
	{
		printf("Point - > (%.3f,%.3f)\n",x,y);
	}
};

double operator * (Vector a,Vector b)
{return a.x*b.y-a.y*b.x;}

Vector operator + (Vector a,Vector b)
{Vector ret;ret.x=a.x+b.x;ret.y=a.y+b.y;return ret;}

Vector operator - (Vector a,Vector b)
{Vector ret;ret.x=a.x-b.x;ret.y=a.y-b.y;return ret;}

Point operator + (Point a,Vector b)
{Point ret;ret.x=a.x+b.x;ret.y=a.y+b.y;return ret;}

Vector operator * (Vector a,double b)
{Vector ret;ret.x=a.x*b;ret.y=a.y*b;return ret;}

Vector operator - (Point a,Point b)
{Vector ret;ret.x=a.x-b.x;ret.y=a.y-b.y;return ret;}

double dot (Vector a,Vector b)
{return a.x*b.x+a.y*b.y;}

double len(Vector a)
{return sqrt(dot(a,a));}

int n,l,top,sta[1005];

Point a[1005];

bool cmp(Point a,Point b)
{return fabs(a.x-b.x)<eps?a.y<b.y:a.x<b.x;}

int main()
{
	scanf("%d%d",&n,&l);
	F(i,1,n) scanf("%lf%lf",&a[i].x,&a[i].y);
	sort(a+1,a+n+1,cmp);
	sta[++top]=1;
	F(i,2,n)
	{
		while (top>=2&&((a[i]-a[sta[top]])*(a[sta[top]]-a[sta[top-1]]))<0) top--;
		sta[++top]=i;
	}
	D(i,n-1,1)
	{
		while (top>=2&&((a[i]-a[sta[top]])*(a[sta[top]]-a[sta[top-1]]))<0) top--;
		sta[++top]=i;
	}
	double ans=0;
	F(i,2,top)
	{
		ans+=len(a[sta[i]]-a[sta[i-1]]);
//		(a[sta[i]]-a[sta[i-1]]).print();
	}
	ans+=2.0*l*pi;
//	printf("%.6f\n",pi);
//	printf("%.6f\n",2.0*l*pi);
	printf("%d\n",(int)(ans+0.5));
}