poj 3122（二分查找）

Pie

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 13564		Accepted: 4650		Special Judge

Description

My birthday is coming up and traditionally I'm serving pie. Not just one pie, no, I have a number N of them, of various tastes and of various sizes. F of my friends are coming to my party and each of them gets a piece of pie. This should be one piece of one pie, not several small pieces since that looks messy. This piece can be one whole pie though.

My friends are very annoying and if one of them gets a bigger piece
than the others, they start complaining. Therefore all of them should
get equally sized (but not necessarily equally shaped) pieces, even if
this leads to some pie getting spoiled (which is better than spoiling
the party). Of course, I want a piece of pie for myself too, and that
piece should also be of the same size.

What is the largest possible piece size all of us can get? All the
pies are cylindrical in shape and they all have the same height 1, but
the radii of the pies can be different.

Input

One line with a positive integer: the number of test cases. Then for each test case:

• One line with two integers N and F with 1 ≤ N, F ≤ 10 000: the number of pies and the number of friends.
• One line with N integers ri with 1 ≤ ri ≤ 10 000: the radii of the pies.

Output

For
each test case, output one line with the largest possible volume V such
that me and my friends can all get a pie piece of size V. The answer
should be given as a floating point number with an absolute error of at
most 10⁻³.

Sample Input

3
3 3
4 3 3
1 24
5
10 5
1 4 2 3 4 5 6 5 4 2

Sample Output

25.1327
3.1416
50.2655

Source

Northwestern Europe 2006

 #include<iostream>
 #include<cstdio>
 #include<algorithm>
 #include<cstring>
 #include<cstdlib>
 #include<cmath>
 #include<vector>
 #include<iomanip>
 #include<queue>
 #include<stack>
 using namespace std;
 #define N 10000
 #define PI 3.1415926535897932384626
 double r[N],v,d,c,ma;
 int main(){
     //freopen("in.txt","r",stdin);
     std::ios::sync_with_stdio(false);
     cin>>c;
     while(c--){
         int n,f;
         cin>>n>>f;
         f++;
         ma=0.0;
         for(int i=;i<n;i++){
             cin>>r[i];
             r[i]*=r[i];
             if(ma<r[i]) ma=r[i];
         }
         double up,low,mid;
         low=0.0;up=ma;
         while(up-low>1e-){
             mid=(up+low)/;
             int num=;
             for(int i=;i<n;i++)
                 num+=(int)(r[i]/mid);
             if(num>=f)
                 low=mid;
             else
                 up=mid;
         }
         cout<<fixed<<setprecision()<<mid*PI<<endl;
     }
     return ;
 }