Pie（hdu 1969 二分查找）

Pie

Time Limit: 5000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 7302    Accepted Submission(s): 2732

Problem 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

4
3 3
4 3 3
1 24
5
10 5
1 4 2 3 4 5 6 5 4 2
2 1
1000 1000

 

Sample Output

25.1327

3.1416

50.2655

3141592.6536

 

因为ri最大可以到1000，最大的面积就可能3141592.6536，所以π精度需要提高

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
#define Max 10000+10
#define INF 10000000000
#define P  3.1415926535898
using namespace std;
double a[Max];
int n,f;
int search(double size)
{
    int num=0;
    for(int i=0;i<n;i++)
        num+=int(a[i]/size);
    return num;
}
int main()
{
    int T,i,j,e;
    freopen("in.txt","r",stdin);
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d%d",&n,&f);
        f++;
        for(i=0;i<n;i++)
        {
            scanf("%d",&e);
            a[i]=e*e*P;
        }
        double mid,l=0,r=INF,k;
        for(i=0;i<1000;i++)
        {
            mid=(l+r)/2;
            if(search(mid)>=f) k=mid,l=mid;
            else r=mid;
        }
        printf("%0.4lf
",k);
    }
}