hdu 3847 Trash Removal 2011WorldFinal 凸包

/*求出多边形最窄的地段长度枚举边，求出所有点中到边的距离最大的值这些值中最小的就是答案*/#include <cstdio>#include <cstring>#include <cmath>#include <cstdlib>const int MAXN = 109;const double eps = 1e-4;struct point{    double x,y;}p[MAXN],h[MAXN];inline double distance(const point &p1,const point &p2){    return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));}//   求两点之间的距离inline double multiply(const point &sp,const point &ep,const point &op){      return ((sp.x-op.x)*(ep.y-op.y)-(ep.x-op.x)*(sp.y-op.y));}//判断sp,ep，op是否满足左转int cmp(const void *a,const void *b){//按极角排序    point *p1 = (point *)a;    point *p2 = (point *)b;    double t = multiply(*p2,*p1,p[0]);    if(t>eps) return 1;    else if(fabs(t)<=eps)     {    if(distance(p[0],*p1)>distance(p[0],*p2)) return 1;    else return -1;    }    else return -1;}void anglesort(point p[],int n){//找到最左下方的点    int i,k=0;    point temp;    for(i=1;i<n;i++)        if(p[i].x<p[k].x ||( fabs(p[i].x-p[k].x)<eps && (p[i].y<p[k].y)))            k=i;    temp=p[0],p[0]=p[k],p[k]=temp;    qsort(p+1,n-1,sizeof(point),cmp);}void Graham_scan(point p[],point ch[],int n,int &len){//建立凸包    int i,top=2;    anglesort(p,n);    if(n<3){        for(i=0,len=n;i<n;i++) ch[i]=p[i];        return;    }    ch[0]=p[0],ch[1]=p[1],ch[2]=p[2];    p[n]=p[0];    for(i=3;i<n;i++){        while(multiply(p[i],ch[top],ch[top-1])>=eps) top--;        ch[++top]=p[i];    }    len=top+1;}double judge(point _x,point _y,int len){    double res=0;    for(int i=0;i<len;i++)    {        double tmp=fabs(multiply(h[i],_x,_y))/distance(_x,_y);//面积法求出距离        if(tmp>res)        res=tmp;    }    return res;}double solve(int len){    h[len]=h[0];    double ans=1<<30;    for(int i=0;i<len;i++)    {        double tmp=judge(h[i],h[i+1],len);//枚举边        if(tmp<ans)        ans=tmp;    }    return ans;}int main(){    int n,len;    int d=0;    while(scanf("%d",&n),n)    {        for(int i=0;i<n;i++) scanf("%lf %lf",&p[i].x,&p[i].y);        Graham_scan(p,h,n,len);        printf("Case %d: %.2lf\n",++d,solve(len)+0.005);    }    return 0;}