uva 10012

题目意思：  给定m个圆的半径，现在要求找到一个矩形使得每一个球都以地面相切，要求输出最小的矩阵的长度

 #include <iostream>
 #include <algorithm>
 #include <cstring>
 #include <cstdlib>
 #include <cstdio>
 #include <cmath>
 using namespace std;
 int num;
 bool vis[];
 double a[], c[], l[], _max;
 double sqr(double r)
 {
     return r*r;
 }

 void dfs(int cnt, double len)
 {
     if(len > _max)
         return ;
     if(cnt == num)
     {
         double ll = c[];
         len += c[cnt - ];
         for(int i = ; i < num - ; i++)
             if(l[i] + c[i] > len)
                 len = l[i] + c[i];
         for(int i = ; i < num; i++)
             if(c[i] - l[i] > ll)
                 ll = c[i] - l[i];
         len += ll;
         if(len < _max)
             _max = len;
         return ;
     }
     for(int i = ; i < num; i++)
     {
         if(vis[i]) continue;
         vis[i] = true;
         c[cnt] = a[i];
         l[cnt] = c[cnt];
         for(int j = cnt - ; j >= ; j--)
         {
             double dis = l[j] + sqrt(sqr(c[j]+c[cnt])-sqr(c[j]-c[cnt]));
             if(dis > l[cnt])
                 l[cnt] = dis;
         }
         dfs(cnt + , l[cnt]);
         vis[i] = false;
     }
 }
 int main()
 {
     int n;
     scanf("%d", &n);
     memset(vis, , sizeof(vis));
     while(n--)
     {
         _max = 0x7FFFFFFF;
         scanf("%d", &num);
         for(int i = ; i < num; i++)
             scanf("%lf", &a[i]);
         for(int i = ; i < num; i++)
         {
             vis[i] = true;
             l[] = ;
             c[] = a[i];
             dfs(, );
             vis[i] = false;
         }
         printf("%.3lf\n", _max);
     }
     return ;
 }