两圆相交，求相交的面积模板

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#include<iostream>
#include <cstdio>
#include<cmath>
using namespace std;

#define pi acos(-1.0)

typedef struct node
{
    int x;
    int y;
}point;

double AREA(point a, double r1, point b, double r2)
{
    double d = sqrt((a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y));
    if (d >= r1+r2)
        return 0;
    if (r1>r2)
    {
        double tmp = r1;
        r1 = r2;
        r2 = tmp;
    }
    if(r2 - r1 >= d)
        return pi*r1*r1;
    double ang1=acos((r1*r1+d*d-r2*r2)/(2*r1*d));
    double ang2=acos((r2*r2+d*d-r1*r1)/(2*r2*d));
    return ang1*r1*r1 + ang2*r2*r2 - r1*d*sin(ang1);
}

int main()
{
    int t;
    scanf("%d", &t);
    for(int cas=1; cas<=t; cas++)
    {
        point a, b;    //圆a，b的圆心
        int ra, rb;    //圆a，b的半径
        scanf("%d%d%d%d%d%d", &a.x, &a.y, &ra, &b.x, &b.y, &rb);
        printf("Case %d: %.10f\n", cas, AREA(a, ra, b, rb));
    }
    return 0;
}

详细题目参见：LightOJ——1118