HDU5120(平面几何)

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求两个圆环的相交面积。

容易知道相交面积=两个大圆相交面积+两个小圆相交面积-2*大圆和小圆相交面积。

#include<cstdio>#include<cstring>#include<cmath>#include<algorithm>#include<iostream>using namespace std;double x1,ya,x2,y2;double dis;double s1,s2,s3;double R,r;double sov(double R,double r) {    if(dis>=r+R) return 0.0;    if(dis==0||dis<=R-r) {        return acos(-1)*r*r;    }    double x=(R*R-r*r+dis*dis)/2.0/dis;    double y=(r*r-R*R+dis*dis)/2.0/dis;    double seta1=2*acos(x/R);    double seta2=2*acos(y/r);    double ans=seta1*R*R/2.0+seta2*r*r/2.0;    double h=sqrt(R*R-x*x);    ans-=dis*h;    return ans;}int main(){    int t;    int kase=0;    scanf("%d",&t);    while(t--) {        scanf("%lf%lf",&r,&R);        scanf("%lf%lf%lf%lf",&x1,&ya,&x2,&y2);        dis=sqrt((x1-x2)*(x1-x2)+(ya-y2)*(ya-y2));        s1=sov(R,R);        s2=sov(R,r);        s3=sov(r,r);        double tot=s1-2*s2+s3;        printf("Case #%d: ",++kase);        printf("%.6f\n",tot);    }    return 0;}

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