poj 2546 圆和圆相交的面积交模板

#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <algorithm>
#define repf(i,a,b) for(int i=(a);i<=(b);i++)

using namespace std;

typedef long long LL;
const double PI = 

struct Round
{
    double x , y;
    double r;
}r[2];

double dis ( Round a , Round b )
{
    return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
}

double solve ( Round a , Round b )
{
    double d = dis(a,b);
    if ( d >= a.r + b.r ) return 0;
    if ( d <= fabs(a.r - b.r))
    {
        double r = a.r < b.r ? a.r : b.r;
        return PI * r * r;
    }
    double ang1 = acos((a.r * a.r + d * d - b.r * b.r)/2. / a.r / d );
    double ang2 = acos((b.r * b.r + d * d - a.r * a.r)/2. / b.r / d );
    double ret = ang1 * a.r * a.r + ang2 * b.r * b.r - d * a.r * sin(ang1);
    return ret;
}

int main ( )
{
    while ( ~scanf ("%lf%lf%lf%lf%lf%lf" , 
                &r[0].x , &r[0].y , &r[0].r ,&r[1].x , &r[1].y , &r[1].r ))
     {
        printf( "%.3f\n" , solve( r[0] , r[1]));
     } 
     return 0;
}