UESTC1713 无关青云路，无关诗书，无你处，无江湖

题意：给出两个圆的坐标求两圆相交的面积

题解：两个圆相交，包含，相离，相切等情况，判断两个圆心的距离与半径的关系，相交的部分可以看作是两个扇形减去菱形的面积

#include <stdio.h>
#include <math.h>
#define PI acos(-1)
double x1,x2,yy,y2,R,r,s1,s2,p,s3,l, s5,s4;
int main(){
    int T;
    scanf("%d", &T);
    while(T--){
        scanf("%lf%lf%lf%lf%lf%lf", &x1, &yy, &r, &x2, &y2, &R);
        l = sqrt((x1-x2)*(x1-x2)+(yy-y2)*(yy-y2));
        //cout<<l<<endl;
        if(R<r) {
            s5 = R;
            R = r;
            r = s5;
        }
        if(R >= l+r) printf("%.6f
", r*r*PI);
        else if(l >= R+r) printf("%.6f
", 0);
        else{
            s1 = acos((r*r+l*l-R*R)/2/r/l);
            s2 = acos((R*R+l*l-r*r)/2/R/l);
            s3 = cos(s1)*r*sin(s1)*r;
            s4 = cos(s2)*R*sin(s2)*R;
            s1 = r*r*s1;
            s2 = R*R*s2;
            printf("%f
", s1-s3+s2-s4);
        }
    }
    return 0;
}