多边形面积交、并模板

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#include<cstdio>#include<cmath>#include<cstring>#include<iostream>#include<algorithm>#include<cstdlib>#include<queue>#include<map>#include<stack>#include<set>using namespace std;const int maxn=555;const int maxisn=10;const double eps=1e-8;const double pi=acos(-1.0);int dcmp(double x){    if(x>eps) return 1;    return x<-eps ? -1 : 0;}inline double Sqr(double x){    return x*x;}struct Point{    double x,y;    Point(){x=y=0;}    Point(double x,double y):x(x),y(y){};    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 dcmp(a.x-b.x)==0&&dcmp(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);    }    friend bool operator < (const Point &a, const Point &b) {        return a.x < b.x || (a.x == b.x && a.y < b.y);    }    inline double dot(const Point &b)const{        return x*b.x+y*b.y;    }    inline double cross(const Point &b,const Point &c)const{        return (b.x-x)*(c.y-y)-(c.x-x)*(b.y-y);    }};Point LineCross(const Point &a,const Point &b,const Point &c,const Point &d){    double u=a.cross(b,c),v=b.cross(a,d);    return Point((c.x*v+d.x*u)/(u+v),(c.y*v+d.y*u)/(u+v));}double PolygonArea(Point p[],int n){     if(n<3) return 0.0;     double s=p[0].y*(p[n-1].x-p[1].x);     p[n]=p[0];     for(int i=1;i<n;i++){        s+=p[i].y*(p[i-1].x-p[i+1].x);     }     return fabs(s*0.5);}double CPIA(Point a[],Point b[],int na,int nb){    Point p[maxisn],temp[maxisn];    int i,j,tn,sflag,eflag;    a[na]=a[0],b[nb]=b[0];    memcpy(p,b,sizeof(Point)*(nb+1));    for(i=0;i<na&&nb>2;++i){        sflag=dcmp(a[i].cross(a[i+1],p[0]));        for(j=tn=0;j<nb;++j,sflag=eflag){            if(sflag>=0) temp[tn++]=p[j];            eflag=dcmp(a[i].cross(a[i+1],p[j+1]));            if((sflag^eflag)==-2)                temp[tn++]=LineCross(a[i],a[i+1],p[j],p[j+1]);        }        memcpy(p,temp,sizeof(Point)*tn);        nb=tn,p[nb]=p[0];    }    if(nb<3) return 0.0;    return PolygonArea(p,nb);}double SPIA(Point a[],Point b[],int na,int nb){    int i,j;    Point t1[4],t2[4];    double res=0.0,if_clock_t1,if_clock_t2;    a[na]=t1[0]=a[0];    b[nb]=t2[0]=b[0];    for(i=2;i<na;i++){        t1[1]=a[i-1],t1[2]=a[i];        if_clock_t1=dcmp(t1[0].cross(t1[1],t1[2]));        if(if_clock_t1<0) swap(t1[1],t1[2]);        for(j=2;j<nb;j++){            t2[1]=b[j-1],t2[2]=b[j];            if_clock_t2=dcmp(t2[0].cross(t2[1],t2[2]));            if(if_clock_t2<0) swap(t2[1],t2[2]);            res+=CPIA(t1,t2,3,3)*if_clock_t1*if_clock_t2;        }    }    return res;//面积交    //return PolygonArea(a,na)+PolygonArea(b,nb)-res;//面积并}Point a[222],b[222];Point aa[222],bb[222];int main(){    double x1,y1,x2,y2;    double x3,y3,x4,y4;    while(scanf("%lf %lf %lf %lf",&x1,&y1,&x2,&y2)!=EOF){        scanf("%lf %lf %lf %lf",&x3,&y3,&x4,&y4);        a[0]=Point(x1,y1);   // 逆时针？？        a[1]=Point(x2,y1);        a[2]=Point(x1,y2);        b[0]=Point(x3,y3);        b[1]=Point(x4,y3);        b[2]=Point(x4,y4);        b[3]=Point(x3,y4);        printf("%.8f\n",fabs(SPIA(a,b,3,4)));        //printf("%.8f\n",ConvexPolygonArea(out,m));    }    return 0;}
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