Anany in the Army(ECPC2019)

因为只能选择一条边进行增长 我们选择最小的一条边进行增加

接着发现增加后的面积要么是单峰函数 要么是单调函数

所以运用三分法去解决

#include<bits/stdc++.h>
using namespace std;
#define lowbit(x) x&(-x)
#define ll long long
int T;
double eps=1e-8;
double s(double aa,double bb,double cc){
	double p=(aa+bb+cc)/2;
	return sqrt(p*(p-aa)*(p-bb)*(p-cc));
}
double  calc()
{
     int a,b,c,k;
	 double minn,l,r;
	  cin>>a>>b>>c>>k;
	  minn=min(a,min(b,c));
	  if(a==minn){
	  	l=a;r=min(b+c,a+k);
	  }
	  else if(b==minn){
	  	l=b;r=min(a+c,b+k);
	  	b=a;
	  }
	  else {
	  	l=c;r=min(a+b,c+k);
	  	c=b;b=a;
	  }
        double mid,midmid;
        while(r - l > eps)
        {
              mid = (l + r)/2.0;
             midmid = (r + mid)/2.0;
            if(s(mid,b,c) >=s(midmid,b,c))
                r = midmid;
            else  l = mid;
        }
    cout<<s(l,b,c)<<endl;
}
int main(){
	freopen("sticks.in","r",stdin);
	cin>>T;
	while(T--)calc();
     return 0;
}