计算几何入门3--poj1113Wall

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裸凸包……直接上代码……

#include<map>#include<set>#include<cmath>#include<queue>#include<cstdio>#include<vector>#include<cstdlib>#include<cstring>#include<iostream>#include<algorithm>using namespace std;const int maxn=10000+10;const double eps=1e-12;int n,l,top=0;double ans;struct point{    double x,y;}p[maxn];point sta[maxn];bool cmp(const point &a,const point &b){    return a.x<b.x||(a.x==b.x&&a.y<b.y);}int comp(double x){    return fabs(x)<eps?0:x>0?1:-1;}double crossx(point a,point b,point c){//ab x ac     return (b.x-a.x)*(c.y-a.y)-(c.x-a.x)*(b.y-a.y);}double cal(point a,point b){    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));}int main(){    while (~scanf("%d%d",&n,&l)){        for (int i=1;i<=n;++i)            scanf("%lf%lf",&p[i].x,&p[i].y);        memset(sta,0,sizeof(sta));        sort(p+1,p+1+n,cmp); top=0; ans=0;                                               sta[++top]=p[1]; sta[++top]=p[2];        for (int i=3;i<=n;++i){            while (top>1&&comp(crossx(sta[top-1],sta[top],p[i]))<0) top--;            sta[++top]=p[i];        }        int mid=top; sta[++top]=p[n]; sta[++top]=p[n-1];        for (int i=n-2;i>=1;i--){            while (top>mid&&comp(crossx(sta[top-1],sta[top],p[i]))<0) top--;            sta[++top]=p[i];        }        for (int i=2;i<=top;++i)             ans+=cal(sta[i],sta[i-1]);        //for (int i=1;i<=top;++i) printf("%lf %lf\n",sta[i].x,sta[i].y);        //ans+=cal(sta[1],sta[top]);        double Sy=2*l*3.1415926535; ans+=Sy;        printf("%.0f\n",ans);    }}

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