poj1927Area in Triangle

链接

物理渣只能搜题解了。。

分三种情况

1、len>=a+b+c

2、len<内切圆半径 圆的面积是最大的 --》以len为周长的圆

3、看这篇http://blog.sina.com.cn/s/blog_6a46cc3f0100tujn.html

#include <iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<stdlib.h>
#include<vector>
#include<cmath>
#include<queue>
#include<set>
using namespace std;
#define N 100000
#define LL long long
#define INF 0xfffffff
const double eps = 1e-8;
const double pi = acos(-1.0);
const double inf = ~0u>>2;
int dcmp(double x)
{
    if(fabs(x)<eps) return 0;
    else return x<0?-1:1;
}
int main()
{
    double a,b,c,l;
    int kk = 0;
    while(scanf("%lf%lf%lf%lf",&a,&b,&c,&l)!=EOF)
    {
        if(fabs(a)<eps&&fabs(b)<eps&&fabs(c)<eps&&fabs(l)<eps) break;
        double p = (a+b+c)/2;
        double area = sqrt(p*(p-a)*(p-b)*(p-c));
        double r = sqrt((p-a)*(p-b)*(p-c)/p);
        double ans ;
        if(dcmp(2*pi*r-l)>=0)
        {
            ans = l*l/(4*pi);
            //cout<<"2"<<endl;
        }
        else if(dcmp(l-a-b-c)>=0)
        {
            ans = area;
            //cout<<"1"<<endl;
        }
        else
        {
            double k = (a+b+c-l)/(a+b+c-2*pi*r);
            r*=k;
            ans = area-area*k*k+pi*r*r;
           // cout<<"3"<<endl;
        }
        printf("Case %d: %.2f
",++kk,ans);
    }
    return 0;
}