最圆点对，（凸包+旋转卡壳）

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#include<iostream>#include<cstdio>#include<algorithm>#include<math.h>#define eps 1e-6#define inf 1e10#define maxn 1000005struct point{    double x,y;}p[maxn],s[maxn];int n;double xmult(point p1,point p2,point p0){    return (p1.x-p0.x)*(p2.y-p0.y)-(p1.y-p0.y)*(p2.x-p0.x);}double max(double a,double b){return a>b? a:b;}bool cmp(const point &a,const point &b ){    if(a.y==b.y)return a.x<b.x;    return a.y<b.y;}int Graham(){    int i;    std::sort(p,p+n,cmp);    s[0]=p[0];    s[1]=p[1];    int top=1;    for(i=0;i<n;i++)    {        while(top>0&& xmult(s[top],p[i],s[top-1])>=0)            top--;        s[++top]=p[i];    }    int mid=top;    for(i=n-2;i>=0;i--)    {        while(top>mid&&xmult(s[top],p[i],s[top-1])>=0)            top--;        s[++top]=p[i];    }    return top;}double rc_tri(){    if(n<3)return 0;    double maxx=0 ,temp;    int i;    int b=1,c=2;    s[n]=s[0];    s[n+1]=s[1];    s[n+2]=s[2];    for(i=0;i<n;i++)    {        while(xmult(s[c+1],s[b],s[i])-(temp=xmult(s[c],s[b],s[i]))>eps)            c=(c+1)%n;        maxx=max(maxx,temp);        while(xmult(s[c],s[b+1],s[i])-(temp=xmult(s[c],s[b],s[i]))>eps)            b=(b+1)%n;        maxx=max(maxx,temp);    }    return maxx;}int main(){    while(~scanf("%d",&n))    {        if(n==-1) break;        int i;        for(i=0;i<n;i++)scanf("%lf%lf",&p[i].x,&p[i].y);        n=Graham();        printf("%.2f\n",rc_tri()/2);    }    return 0;}

hdu3934 poj 2079

#include<stdio.h>#include<string.h>#include<algorithm>#include<math.h>#define maxn 1000005typedef struct{    double x,y;}Point;Point a[maxn];Point stack[maxn];double Distance(Point t1,Point t2){    return sqrt((t1.x-t2.x)*(t1.x-t2.x)+(t1.y-t2.y)*(t1.y-t2.y));}double Cross(Point t1,Point t2,Point t3)    //向量AB（a）与向量AC（b）的叉积,即 a.x*b.y-a.y-b.x;{    return ((t2.x-t1.x)*(t3.y-t1.y)-(t3.x-t1.x)*(t2.y-t1.y));}bool cmp(Point p1,Point p2){    double m=Cross(a[0],p1,p2);    if(m<0) return false; // m小于零时点在里面。    else if(m==0&&Distance(p1,a[0])<Distance(p2,a[0]))      return false;    else return true;}void AREA(int n){    double max=-1;    double area2;    int k,j,i;    for(i=0;i<=n-3;i++)    {        k=0;        for(j=i+1;j<=n-2;j++)        {            if(k<=j) k=j+1;            area2=fabs(Cross(stack[i],stack[j],stack[k]));            if(area2>max) max=area2;            while(k+1<=n-1)            {                double tmp=fabs(Cross(stack[i],stack[j],stack[k+1]));                if(tmp<area2) break;                max=max>tmp?max:tmp;                area2=tmp;                k++;            }        }    }    printf("%.2f\n",max*0.5);}int main(){     //freopen("Input.txt","r",stdin);    int n,i,top;    while(scanf("%d",&n)!=EOF)    {        top=0;        for(i=0;i<n;i++)          scanf("%lf%lf",&a[i].x,&a[i].y);        for(i=0;i<n;i++)  //找基点。            if(a[i].y<a[0].y||(a[i].y==a[0].y&&a[i].x<a[0].x))            {                double a2,b2;                a2=a[0].x; b2=a[0].y;                a[0].x=a[i].x; a[0].y=a[i].y;                a[i].x=a2; a[i].y=b2;            }        std::sort(a+1,a+n,cmp); //按照斜率排序。        stack[top++]=a[0];        stack[top]=a[1];        for(i=2;i<n;i++)        {            while(top>=1&&Cross(stack[top-1],stack[top],a[i])<=0)  //逆时针扫描，向量AB（a）与向量AC（b）的叉积，                top--;                                            //即 a.x*b.y-a.y-b.x;            stack[++top]=a[i];        }        if(top+1<2) { printf("0.00\n");continue ;}        AREA(top+1);    }    return 0;}

poj 3608 求两个不相交凸包的最近距离。

#include<cstdio>#include<iostream>#include<cmath>#include<algorithm>using namespace std;#define N 10002#define EPS 1e-10struct point{    double x;    double y;}pn[N],pm[N];double dis(point a,point b){    return (a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y);}double det(double x1,double y1,double x2,double y2){    return x1*y2-x2*y1;}double cross(point a,point b,point c){    return det(a.x-c.x,a.y-c.y,b.x-c.x,b.y-c.y);}double dot(point a,point b){    return a.x*b.x+a.y*b.y;}double min(double a,double b){    return a>b?b:a;}void adjust(point *p,int n){    for(int i=0;i<n-2;i++)    {        int res=cross(p[i+1],p[i+2],p[i]);        if(res>EPS)return;        else if(res<-EPS)        {            reverse(p,p+n);            return;        }    }}double point_to_seg(point a,point b,point c){    point ab,ac;    ab.x=b.x-a.x;    ab.y=b.y-a.y;    ac.x=c.x-a.x;    ac.y=c.y-a.y;    double f=dot(ab,ac);    if(f<0)return dis(a,c);    double f1=dot(ab,ab);    if(f>f1)return dis(b,c);    f=f/f1;    point d;    d.x=a.x+ab.x*f;    d.y=a.y+ab.y*f;    return dis(d,c);}double seg_to_seg(point a1,point b1,point a2,point b2){    return min(min(point_to_seg(a1,b1,a2),point_to_seg(a1,b1,b2)),min(point_to_seg(a2,b2,a1),point_to_seg(a2,b2,b1)));}double rc(point *p1,int n,point *p2,int m){    int s1=0,s2=0;    for(int i=0;i<n;i++)    {        if(p1[i].y-p1[s1].y<-EPS)        {            s1=i;        }    }    for(int i=0;i<m;i++)    {        if(p2[i].y-p2[s2].y>EPS)        {            s2=i;        }    }    p1[n]=p1[0];    p2[m]=p2[0];    double res,ans=1e20;    for(int i=0;i<n;i++)    {        while((res=cross(p2[s2],p1[s1+1],p1[s1])-cross(p2[s2+1],p1[s1+1],p1[s1]))>EPS)        {            s2=(s2+1)%m;        }        if(res<-EPS)ans=min(ans,point_to_seg(p1[s1],p1[s1+1],p2[s2]));        else ans=min(ans,seg_to_seg(p1[s1],p1[s1+1],p2[s2],p2[s2+1]));        s1=(s1+1)%n;    }    return ans;}int main(){    int n,m;    while(scanf("%d%d",&n,&m)!=EOF)    {        if(n==0&&m==0)break;        for(int i=0;i<n;i++)        {            scanf("%lf%lf",&pn[i].x,&pn[i].y);//第一凸包中的点        }        for(int i=0;i<m;i++)        {            scanf("%lf%lf",&pm[i].x,&pm[i].y); //第二个凸包的点        }        adjust(pn,n);        adjust(pm,m);        printf("%.5f\n",sqrt(min(rc(pn,n,pm,m),rc(pm,m,pn,n))));    }    return 0;}