凸包 poj 1113

求一个多边形  拐弯的地方用圆弧补上

距离>=l

求他的周长

求一个凸包的周长  加2*pi*l

#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<vector>
#include<stack>
#include<math.h>
using namespace std;#define MAXN 1010
#define pi 4*atan(1.0)
class point
{
public:int x,y;point operator -(point b){point c;c.x=x-b.x;c.y=y-b.y;return c;}int operator ^ (point b){return x*b.y-y*b.x;}
};
point x[MAXN];
point ans[MAXN];
stack<point>z;double dis(point a,point b)
{return sqrt(double((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)));
}
bool cmp(point a,point b)
{int tmp=((a-x[0])^(b-x[0]));if(tmp>0)return 1;else if(tmp==0&&dis(x[0],a)<dis(x[0],b))return 1;return 0;
}
int main()
{int n,l;while(scanf("%d%d",&n,&l)!=EOF){while(!z.empty())z.pop();int k=0;for(int i=0;i<n;i++){scanf("%d%d",&x[i].x,&x[i].y);if(x[i].y<x[k].y)//维护一个左下角的点k=i;else if(x[i].y==x[k].y&&x[i].x<x[k].x)k=i;}swap(x[0],x[k]);//交换sort(x+1,x+n,cmp);//极角排序z.push(x[0]); //扫描法z.push(x[1]);point a,b;for(int i=2;i<n;i++){b=z.top();z.pop();a=z.top();while(z.size()>1&&((x[i]-b)^(b-a)) >=0){b=a;z.pop();a=z.top();}z.push(b);z.push(x[i]);}int len=0;while(!z.empty()){ans[len++]=z.top();z.pop();}double ans1=0;for(int i=0;i<len-1;i++)ans1+=dis(ans[i],ans[i+1]);ans1+=dis(ans[len-1],ans[0]);ans1+=2*pi*l;printf("%d\n",(int)(ans1+0.5));//求和4舍5入}return 0;
}