计算几何 模板

//凸包+最远点对
#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<algorithm>
#include<vector>
using namespace std;
const double eps = 1e-8;

int cmp(double x)
{
    if(fabs(x)<eps)
        return 0;
    if(x>0)
        return 1;
    return -1;
}

inline double sqr(double x)
{
    return x*x;
}

struct point
{
    double x,y;
    point(){}
    point(int xx,int yy)
    {
        x=xx;
        y=yy;
    }
    friend point operator + (const point &a,const point &b)
    {
        return point(a.x+b.x,a.y+b.y);
    }
    friend point operator - (const point &a,const point &b)
    {
        return point(a.x-b.x,a.y-b.y);
    }
    friend bool operator == (const point &a,const point &b)
    {
        return cmp(a.x-b.x)==0 && cmp(a.y-b.y)==0;
    }
    void input()
    {
        scanf("%lf%lf",&x,&y);
    }
    double norm()
    {
        return sqrt(sqr(x)+sqr(y));
    }
};
struct polygon_convex
{
    vector<point>P;
    polygon_convex(int Size=0)
    {
        P.resize(Size);
    }

};

bool comp_less(const point &a,const point &b)
{
    return cmp(a.x-b.x)<0 || (cmp(a.x-b.x==0) && cmp(a.y-b.y)<0);
}

double det(point a,point b)
{
    return a.x*b.y-a.y*b.x;
}
double dist(const point &a,const point &b)
{
    return (a-b).norm();
}
long long dd(const point &a,const point &b)
{
    return sqr(a.x-b.x)+sqr(a.y-b.y);
}
polygon_convex convex_hull(vector<point> a)
{
    polygon_convex res(2*a.size()+5);
    sort(a.begin(),a.end(),comp_less);
    a.erase(unique(a.begin(),a.end()),a.end());
    int m=0;
    for(int i=0;i<a.size();++i)
    {
        while(m>1
              &&
              cmp(det( res.P[m-1]-res.P[m-2],a[i]-res.P[m-2] ))<=0)
            --m;
        res.P[m++]=a[i];
    }
    int k=m;
    for(int i=int(a.size())-2;i>=0;--i)
    {
        while(m>k && cmp(det(res.P[m-1]-res.P[m-2],a[i]-res.P[m-2]))<=0)--m;
        res.P[m++]=a[i];
    }
    res.P.resize(m);
    if(a.size()>1)
        res.P.resize(m-1);
    return res;
}

long long convex_diameter(polygon_convex &a,int &First,int &Second)
{
    vector<point> &p = a.P;
    int n=p.size();
    long long maxd=0;
    if(n==1)
    {
        First=Second=0;
        return maxd;
    }
    #define next(i) ((i+1)%n)
    for(int i=0,j=1;i<n;i++)
    {
        while(cmp(det(p[next(i)]-p[i],p[j]-p[i])-det(p[next(i)]-p[i],p[next(j)]-p[i]))<0)
        {
            j=next(j);
        }
        long long d=dd(p[i],p[j]);
        if(d>maxd)
        {
            maxd=d;
            First=i,Second=j;
        }
        d=dd(p[next(i)],p[next(j)]);
        if(d>maxd)
        {
            maxd=d;
            First=i,Second=j;
        }
    }
    return maxd;
}
int n;
vector<point> p;
polygon_convex pc;
point pp;
int main()
{
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
    {
        pp.input();
        p.push_back(pp);
    }
    int x,y;
    pc = convex_hull(p);
    long long dis = convex_diameter(pc,x,y);
    cout<<dis;
}

//圆与多边形面积交
#include<iostream>
#include<cmath>
#include<cstdlib>
#include<cstdio>
#include<cmath>
using namespace std;
const int Max = 1011;
const double PI =acos(-1.0);
const double pi =acos(-1.0);

double ax,ay,bx,by,K;
double cx,cy,tx,ty,R;
int n;

const double eps=1e-8;
int cmp(double x)
{
    if(fabs(x)<eps)
        return 0;
    if(x>0)
        return 1;
    return -1;
}
inline double sqr(double x)
{
    return x*x;
}

struct point
{
    double x,y;
    point(){};
    point(double a,double b):x(a),y(b){}
    friend point operator +(const point &a,const point &b)
    {
        return point(a.x+b.x,a.y+b.y);
    }
    friend point operator -(const point &a,const point &b)
    {
        return point(a.x-b.x,a.y-b.y);
    }
    friend bool operator ==(const point &a,const point &b)
    {
        return (cmp(a.x-b.x)==0)&&(cmp(a.y-b.y)==0);
    }
    friend point operator *(const point &a,const double &b)
    {
        return point(a.x*b,a.y*b);
    }
    friend point operator *(const double &a,const point &b)
    {
        return point(a*b.x,a*b.y);
    }
    friend point operator /(const point &a,const double &b)
    {
        return point(a.x/b,a.y/b);
    }
    double norm()
    {
        return sqrt(x*x+y*y);
    }
};

double det(const point &a,const point &b)
{
    return a.x*b.y-a.y*b.x;
}
double dot(const point &a,const point &b)
{
    return a.x*b.x+a.y*b.y;
}
double dist(const point &a,const point &b)
{
    return (a-b).norm();
}
point rotate_point(const point &a,const double A)
{
    double tx=a.x,ty=a.y;
    return point(tx*cos(A)-ty*sin(A),tx*sin(A)+ty*cos(A));
}

int dcmp(double k){
    return k<-eps?-1:k>eps?1:0;
}

double cross(const point &a,const point &b){
    return a.x*b.y-a.y*b.x;
}
double abs(const point &o){
    return sqrt(dot(o,o));
}
point crosspt(const point &a,const point &b,const point &p,const point &q){
    double a1=cross(b-a,p-a);
    double a2=cross(b-a,q-a);
    return (p*a2-q*a1)/(a2-a1);
}
point res[Max];
double r;
double mysqrt(double n){
    return sqrt(max(0.0,n));
}
void circle_cross_line(const point &a,const point &b,const point &o,double r,point ret[],int &num)
{
    double x0=o.x,y0=o.y;
    double x1=a.x,y1=a.y;
    double x2=b.x,y2=b.y;
    double dx=x2-x1,dy=y2-y1;
    double A=dx*dx+dy*dy;
    double B=2*dx*(x1-x0)+2*dy*(y1-y0);
    double C=(x1-x0)*(x1-x0)+(y1-y0)*(y1-y0)-r*r;
    double delta=B*B-4*A*C;
    num=0;
    if(dcmp(delta)>=0)
    {
        double t1=(-B-mysqrt(delta))/(2*A);
        double t2=(-B+mysqrt(delta))/(2*A);
        if(dcmp(t1-1)<=0&&dcmp(t1)>=0) ret[num++]=point(x1+t1*dx,y1+t1*dy);
        if(dcmp(t2-1)<=0&&dcmp(t2)>=0) ret[num++]=point(x1+t2*dx,y1+t2*dy);
    }
}

double sector_area(const point &a,const point &b){
    double theta=atan2(a.y,a.x)-atan2(b.y,b.x);
    while(theta<=0) theta+=2*PI;
    while(theta>2*PI) theta-=2*PI;
    theta=min(theta,2*PI-theta);
    return r*r*theta/2;
}
double calc(const point &a,const point &b){
    point p[2];
    int num =0;
    int ina=dcmp(abs(a)-r)<0;
    int inb=dcmp(abs(b)-r)<0;
    if(ina)
    {
        if(inb)
        {
            return fabs(cross(a,b))/2.0;
        }
        else
        {
            circle_cross_line(a,b,point(0,0),r,p,num);
            return sector_area(b,p[0])+fabs(cross(a,p[0]))/2.0;
        }
    }
    else
    {
        if(inb)
        {
            circle_cross_line(a,b,point(0,0),r,p,num);
            return sector_area(p[0],a)+fabs(cross(p[0],b))/2.0;
        }
        else
        {
            circle_cross_line(a,b,point(0,0),r,p,num);
            //cout<<"num="<<num<<endl;
            if(num==2)
            {
                //cout<<"num=2"<<endl;
                return sector_area(a,p[0])+sector_area(p[1],b)+fabs(cross(p[0],p[1]))/2.0;
            }
            else
            {
                //cout<<" not in "<<a.x<<" "<<a.y<<" "<<b.x<<" "<<b.y<<endl;
                return sector_area(a,b);
            }
        }
    }
}
double area(){
    double ret=0;
    for(int i=0;i<n;i++){
        int sgn=dcmp(cross(res[i],res[i+1]));
        if(sgn!=0){
            ret+=sgn*calc(res[i],res[i+1]);
            //cout<<"sgn="<<sgn<<" calc="<<calc(res[i],res[i+1])<<endl;
            //cout<<"point "<<res[i].x<<" "<<res[i].y<<" "<<res[i+1].x<<" "<<res[i+1].y<<endl;
            //cout<<"ret="<<ret<<endl;
        }
    }
    return ret;
}



int main()
{
    int it=0;
    while(scanf("%d",&n)==1)
    {
        it++;
        //cout<<"PI="<<PI<<endl;
        scanf("%lf",&K);
        //K=1/K;
        for(int i=0;i<n;i++)
            scanf("%lf%lf",&res[i].x,&res[i].y);
        res[n].x=res[0].x;
        res[n].y=res[0].y;
        scanf("%lf%lf%lf%lf",&ax,&ay,&bx,&by);
        tx=ax+(bx-ax)/(1+K);
        ty=ay+(by-ay)/(1+K);
        cx=ax+(bx-ax)+(bx-ax)*K/(1-K);
        cy=ay+(by-ay)+(by-ay)*K/(1-K);
        cx=(cx+tx)/2;
        cy=(cy+ty)/2;
        R=sqrt((tx-cx)*(tx-cx)+(ty-cy)*(ty-cy));
        r=R;
        for(int i=0;i<=n;i++)
        {
            res[i].x-=cx;
            res[i].y-=cy;
            //cout<<"res["<<i<<"].x="<<res[i].x<<endl;
            //cout<<"res["<<i<<"].y="<<res[i].y<<endl;
        }
        printf("Case %d: %.8f
",it,fabs(area()));
    }
}