C++(clang++11) 解法, 执行用时: 7ms, 内存消耗: 400K, 提交时间: 2020-11-20 17:39:09

#include<bits/stdc++.h>
using namespace std;
const double pi=3.1415926536;
int main(){
   // freopen("7.in","r",stdin);
   // freopen("7.out","w",stdout);
    double x,y,r;
    cin>>x>>y>>r;
    x/=2,y/=2;
    if(x>y)swap(x,y);

    double ma=(sqrt(x*x+y*y));
    if(r>=ma)printf("%.2lf",4*x*y);
    else if(r<=x)printf("%.2lf",pi*r*r);
    else if(r<=y){
        double h=sqrt(r*r-x*x);
        printf("%.2lf",2*asin(x/r)*r*r+2*h*x);
    }
    else{
        double h1=sqrt(r*r-x*x),h2=sqrt(r*r-y*y);
        printf("%.2lf",(2*pi-4*acos(x/r)-4*acos(y/r))*r*r/2+2*h1*x+2*h2*y);
    }
}