poj 3608 Bridge Across Islands 两凸包间最近距离

/**
旋转卡壳，，
**/
#include <iostream>
#include <algorithm>
#include <cmath>
#include <cstdio>
using namespace std;

const double eps = 1e-8;
struct point {
    double x,y;
    point(double x=0,double y =0):x(x),y(y){}
};

int dcmp(double x){
    if(fabs(x)<eps)
        return 0;
    else
        return x<0?-1:1;
}

point p[10020],p1[10020];
point q[10020],q1[10020];
int maxid,minid;
int N,M;
typedef point Vector;

Vector operator -(point a,point b){
    return Vector(a.x-b.x,a.y-b.y);
}

double cross(Vector a,Vector b){
    return a.x*b.y-a.y*b.x;
}

double dot(Vector a,Vector b){
    return a.x*b.x+a.y*b.y;
}
bool  cmp(point a,point b){
    if(a.x==b.x)
        return a.y<b.y;
    return a.x<b.x;
}

bool operator ==(const point &a,const point &b){
    return dcmp(a.x-b.x)==0&&dcmp(a.y-b.y)==0;
}

double length(Vector a){
    return sqrt(a.x*a.x+a.y*a.y);
}

int convexHull(point *p,int n,point *ch){
    sort(p,p+n,cmp);
    int m =0;
    for(int i=0;i<n;i++){
        while(m>1&&cross(ch[m-1]-ch[m-2],p[i]-ch[m-2])<=0)
            m--;
        ch[m++] = p[i];
    }
    int k =m;
    for(int i = n-2;i>=0;i--){
        while(m>k&&cross(ch[m-1]-ch[m-2],p[i]-ch[m-2])<=0)
            m--;
        ch[m++] = p[i];
    }
    if(n>1) m--;
    return m;
}

double distanceToSegment(point p,point a,point b){
    if(a==b)
        return length(p-a);
    Vector v1 = b-a,v2 = p-a, v3 = p-b;
    if(dcmp(dot(v1,v2))<0)
        return length(v2);
    else if(dcmp(dot(v1,v3))>0)
        return length(v3);
    else
        return fabs(cross(v1,v2))/length(v1);
}

double distanceBetweenSegment(point a,point b,point c,point d){
    return min(min(distanceToSegment(a,c,d),distanceToSegment(b,c,d)),min(distanceToSegment(c,a,b),distanceToSegment(d,a,b)));
}

void getMaxAndMin(int &maxid,int &minid){
    maxid =0;
    minid =0;
    for(int i=1;i<N;i++){
        if(p1[i].y<p1[minid].y)
            minid =i;
    }
    for(int i=0;i<M;i++){
        if(q1[i].y>q1[maxid].y)
            maxid = i;
    }
}

double solve(point *p,point *q,int minid,int maxid,int N,int M){
    double temp,ret = 1e5;
    p[N] = p[0];
    q[M] = q[0];
    for(int i=0;i<N;i++){
        while(temp = dcmp(cross(q[maxid]-q[maxid+1],p[minid+1]-p[minid]))>0){
            maxid = (maxid+1)%M;
        }
        if(temp<0)
            ret = min(ret,distanceToSegment(q[maxid],p[minid],p[minid+1]));
        else
            ret = min(ret,distanceBetweenSegment(p[minid],p[minid+1],q[maxid],q[maxid+1]));
        minid = (minid+1)%N;
    }
    return ret;
}

int main()
{

    while(cin>>N>>M){
        if(N==0&&M==0)
            break;
        for(int i=0;i<N;i++)
            cin>>p[i].x>>p[i].y;
        for(int i=0;i<M;i++)
            cin>>q[i].x>>q[i].y;
        N = convexHull(p,N,p1);
        M = convexHull(q,M,q1);
        getMaxAndMin(maxid,minid);
        double ans = solve(p1,q1,minid,maxid,N,M);
        printf("%.5lf
",ans);
    }
    return 0;
}