LA 3635 Pie

题意：给出n个圆，分给n+1个人，求每个人最多能够得到多大面积的圆

二分每个人得到的圆的面积

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include <cmath>
 #include<stack>
 #include<vector>
 #include<map>
 #include<set>
 #include<queue>
 #include<algorithm>
 using namespace std;

 typedef long long LL;
 const int INF = (<<)-;
 const int mod=;
 const int maxn=;
 const double pi = 3.14159265359;

 double a[maxn];
 int n,f;

 int ok(double x){
     int ans = ;
     for(int i = ;i <= n;i++){
         ans += (int) (a[i] / x);
     }
     return ans >= f+;
 }

 int main(){
     int T;
     scanf("%d",&T);
     while(T--){
         scanf("%d %d",&n,&f);
         double lb,ub,mid;
         ub = -;
         for(int i =;i <= n;i++){
             scanf("%lf",&a[i]);
             a[i] = a[i] * a[i];
             ub = max(ub,a[i]);
         }

          lb = 0.000;
         for(int i = ;i<=;i++){
             mid = (lb + ub) / ;
             if(ok(mid)) lb = mid;
             else ub = mid;
         //    printf("lb = %lf  ub = %lf  mid = %lf\n",lb,ub,mid);
         }
         printf("%.4lf\n",lb * pi);
     }
     return ;
 }