和矩形相关的操作

#include <cstdio>
#include <cstring>
#include <vector>
#include <cmath>
#define PI 3.141592654
#define eps 1e-8
using namespace std;
/*********************************************************************/
struct point
{
    int x,y;
    point() {}
    point(int _x,int _y):x(_x),y(_y) {}
} p[40];
double getdis(int a,int b)///两点之间的距离
{
    return sqrt((double)(p[b].y-p[a].y)*(p[b].y-p[a].y)+(p[b].x-p[a].x)*(p[b].x-p[a].x));
}
struct rectangle
{
    int a,b,c,d;
    double h,w,l;
    rectangle(int _a,int _b,int _c,int _d):a(_a),b(_b),c(_c),d(_d)
    {
        h=getdis(_a,_b);
        w=getdis(_a,_c);
        l=getdis(_a,_d);
        if(h>w) swap(h,w);
        if(w>l) swap(w,l);
        if(h>w) swap(h,w);
    }
};
bool isRightAngle(int a,int b,int c) ///推断ab与ac是否构成直角
{
    if((p[b].y-p[a].y)*(p[c].y-p[a].y)==-1*(p[b].x-p[a].x)*(p[c].x-p[a].x))
        return true;
    return false;
}
bool isRectangle(int a,int b,int c,int d) ///推断a,b,c,d是否构成矩形
{
    int rightAngle=0;
    if(isRightAngle(a,b,c)||isRightAngle(a,b,d)||isRightAngle(a,c,d))
        rightAngle++;
    if(isRightAngle(b,a,c)||isRightAngle(b,a,d)||isRightAngle(b,c,d))
        rightAngle++;
    if(isRightAngle(c,a,b)||isRightAngle(c,a,d)||isRightAngle(c,b,d))
        rightAngle++;
    if(isRightAngle(d,a,b)||isRightAngle(d,a,c)||isRightAngle(d,b,c))
        rightAngle++;
    if(rightAngle==4)
        return true;
    else
        return false;
}
double getAngle(int a,int b,int c)///得到ab与ac的夹角
{
    double x=getdis(a,b);
    double y=getdis(a,c);
    double z=getdis(b,c);
    double l=(x+y+z)/2;
    double area=sqrt(l*(l-x)*(l-y)*(l-z));
    if(x*x+y*y-z*z<-eps)
        return (asin(2*area/(x*y))+PI/2);
    else
        return asin(2*area/(x*y));
}
bool isInside(rectangle t,int p)///推断p是否在矩形t内部
{
    double ans=0;
    if(getdis(t.a,t.b)<t.l-eps)
        ans+=getAngle(p,t.a,t.b);
    if(getdis(t.a,t.c)<t.l-eps)
        ans+=getAngle(p,t.a,t.c);
    if(getdis(t.a,t.d)<t.l-eps)
        ans+=getAngle(p,t.a,t.d);
    if(getdis(t.b,t.c)<t.l-eps)
        ans+=getAngle(p,t.b,t.c);
    if(getdis(t.b,t.d)<t.l-eps)
        ans+=getAngle(p,t.b,t.d);
    if(getdis(t.c,t.d)<t.l-eps)
        ans+=getAngle(p,t.c,t.d);
    if(ans-2*PI>-eps&&ans-2*PI<eps)
        return true;
    else return false;
}
bool onSement(int a,int b,int c)///推断c是否在ab线段上
{
    if((p[c].x-p[a].x)*(p[b].y-p[a].y)==(p[b].x-p[a].x)*(p[c].y-p[a].y)&&min(p[a].x,p[b].x)<=p[c].x&&p[c].x<=max(p[a].x,p[b].x)&&
            min(p[a].y,p[b].y)<=p[c].y&&p[c].y<=max(p[a].y,p[b].y))
        return true;
    else
        return false;
}
bool isInEdge(rectangle t,int q)///推断q是否在矩形边框上
{
    if(getdis(t.a,t.b)<t.l-eps&&onSement(t.a,t.b,q))
        return true;
    if(getdis(t.a,t.c)<t.l-eps&&onSement(t.a,t.c,q))
        return true;
    if(getdis(t.a,t.d)<t.l-eps&&onSement(t.a,t.d,q))
        return true;
    if(getdis(t.b,t.c)<t.l-eps&&onSement(t.b,t.c,q))
        return true;
    if(getdis(t.b,t.d)<t.l-eps&&onSement(t.b,t.d,q))
        return true;
    if(getdis(t.c,t.d)<t.l-eps&&onSement(t.c,t.d,q))
        return true;
    return false;
}
double getArea(rectangle t)///得到矩形的面积
{
    return t.h*t.w;
}
/************************************************************************/
vector<rectangle> vc;
int n;
int main()
{
    while(scanf("%d",&n)!=EOF&&n!=0)
    {
        for(int i=0; i<n; ++i)
            scanf("%d%d",&p[i].x,&p[i].y);
        vc.clear();
        for(int i=0; i<n; ++i)
            for(int j=i+1; j<n; ++j)
                for(int u=j+1; u<n; ++u)
                    for(int v=u+1; v<n; ++v)
                        if(isRectangle(i,j,u,v))
                            vc.push_back(rectangle(i,j,u,v));
        double ans=0;
        int tsize=vc.size();
        for(int i=0; i<tsize; ++i)
            for(int j=i+1; j<tsize; ++j)
            {
                if(isInEdge(vc[i],vc[j].a)||isInEdge(vc[i],vc[j].b)||isInEdge(vc[i],vc[j].c)||isInEdge(vc[i],vc[j].d))
                    continue;
                if(isInEdge(vc[j],vc[i].a)||isInEdge(vc[j],vc[i].b)||isInEdge(vc[j],vc[i].c)||isInEdge(vc[j],vc[i].d))
                    continue;
                if(isInside(vc[i],vc[j].a)&&isInside(vc[i],vc[j].b)&&isInside(vc[i],vc[j].c)&&isInside(vc[i],vc[j].d)){
                    ans=max(ans,getArea(vc[i]));
                    continue;
                }
                if(isInside(vc[j],vc[i].a)&&isInside(vc[j],vc[i].b)&&isInside(vc[j],vc[i].c)&&isInside(vc[j],vc[i].d)){
                    ans=max(ans,getArea(vc[j]));
                    continue;
                }
                if(isInside(vc[i],vc[j].a)||isInside(vc[i],vc[j].b)||isInside(vc[i],vc[j].c)||isInside(vc[i],vc[j].d))
                    continue;
                if(isInside(vc[j],vc[i].a)||isInside(vc[j],vc[i].b)||isInside(vc[j],vc[i].c)||isInside(vc[j],vc[i].d))
                    continue;
                ans=max(ans,getArea(vc[i])+getArea(vc[j]));
            }
        if(ans>=-eps&&ans<=eps)
            printf("imp
");
        else
            printf("%d
",(int)(ans+0.5));
    }
    return 0;
}