hdu 1798 求相交圓面積

hdu 1798
詳細解釋
坑點：計算三角形面積不能用d求，會wa，不知道爲什麼

#include<bits/stdc++.h>
#define inf  0x7fffffff
#define linf 0x7fffffffffffffff
#define fil(x,y) memset(x,y,sizeof(x))
#define fup(i,x,y) for(int i=(x);i<=(y);i++)
#define fdn(i,x,y) for(int i=(x);i>=(y);i--)
#define sp(x) setprecision(x)
#define sd(n) scanf("%d",&n)
#define sdd(n,m) scanf("%d%d",&n,&m)
#define sddd(n,m,k) scanf("%d%d%d",&n,&m,&k)
#define sld(n) scanf("%lld",&n)
#define sldd(n,m) scanf("%lld%lld",&n,&m)
#define slddd(n,m,k) scanf("%lld%lld%lld",&n,&m,&k)
#define sf(n) scanf("%lf",&n)
#define sff(n,m) scanf("%lf%lf",&n,&m)
#define sfff(n,m,k) scanf("%lf%lf%lf",&n,&m,&k)
#define sc(n) scanf("%s",n)
#define lowbit(x) (x&(-x))
#define pf(x) printf("%d\n",x)
#define pfl(x) printf("%lld\n",x)
#define pff(x) printf("%lf\n",x)
#define debug printf("!!\n");
#define N 1000005
#define M 4000009
#define pi acos(-1)
#define eps 1e-2
//cout.setf(ios::fixed);
//freopen("out.txt","w",stdout);// freopen("in.txt","r",stdin);
using namespace std;
typedef long long  ll;
typedef double db;
using namespace std;
typedef long long ll;
using namespace std;
struct node
{
    db x,y,r;
}l,r;
db dis(db a,db b,db c,db d)
{
    return pow(a-c,2)+pow(b-d,2);
}
db area()
{
    db d=sqrt(dis(l.x,l.y,r.x,r.y));
    if(l.r>r.r) swap(l,r);
    db r1=l.r,r2=r.r;
    if(d>=r1+r2) return 0;
    if(fabs(r2-r1)>=d) return pi*r1*r1;
    db ang1=acos((r1*r1+d*d-r2*r2)/(2*r1*d));
    db ang2=acos((r2*r2+d*d-r1*r1)/(2*r2*d));
    return ang1*r1*r1+ang2*r2*r2-r1*r1*sin(ang1*2)/2-r2*r2*sin(ang2*2)/2;
}
int main()
{

    while(~sfff(l.x,l.y,l.r))
    {
    sfff(r.x,r.y,r.r);
    printf("%0.3lf\n",area());
    }
    return 0;
}