凸包（旋转卡壳求最远点）

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计算几何之凸包(一) {卷包裹算法}

http://www.cnblogs.com/Booble/archive/2011/02/28/1967179.html#3229390

计算几何之凸包(二) {更高效的算法}

http://www.cnblogs.com/Booble/archive/2011/03/10/1980089.html

计算几何之凸包(三) {旋转卡壳初步}

http://www.cnblogs.com/Booble/archive/2011/04/03/2004865.html

快速凸包

QuickHull#include <iostream>#include <math.h>#define maxn 100000#define zero 1e-12#define sgn(x) (fabs(x)<zero?0:(x>0?1:-1))#define cross(a,b,c) ((b.x-a.x)*(c.y-a.y)-(b.y-a.y)*(c.x-a.x))#define cmp(a,b) (a.x<b.x || sgn(a.x-b.x)==0 && a.y<b.y)using namespace std;struct point{    double x,y;}p[maxn];double s[maxn];void hull(int l,int r,point a,point b){    int x=l,i=l-1,j=r+1,k;    for (k=l;k<=r;k++){        double temp=sgn(s[x]-s[k]);        if (temp<0 || temp==0 && cmp(p[x],p[k])) x=k;    }    point y=p[x];    for (k=l;k<=r;k++){        s[++i]=cross(p[k],a,y);        if (sgn(s[i])>0) swap(p[i],p[k]); else i--;    }    for (k=r;k>=l;k--){        s[--j]=cross(p[k],y,b);        if (sgn(s[j])>0) swap(p[j],p[k]); else j++;    }    if (l<=i) hull(l,i,a,y);    printf("%.4lf %.4lf\n",y.x,y.y);    if (j<=r) hull(j,r,y,b);}int main(){    freopen("CH2D.in","r",stdin);    freopen("CH2D1.out","w",stdout);    int n,i,x=0;    scanf("%d",&n);    for (i=1;i<=n;i++){        scanf("%lf %lf",&p[i].x,&p[i].y);        if (x==0 || cmp(p[i],p[x])) x=i;    }    swap(p[1],p[x]);    printf("%.4lf %.4lf\n",p[1].x,p[1].y);    hull(2,n,p[1],p[1]);    return 0;}

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