hdoj 1969 Pie【二分】

Pie

Time Limit: 5000/1000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 6320 Accepted Submission(s):
2383


[align=left]Problem Description[/align]
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.

[align=left]Input[/align]
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.

[align=left]Output[/align]
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).

[align=left]Sample Input[/align]

3

3 3
4 3 3
1 24

5

10 5

1 4 2 3 4 5 6 5 4 2

[align=left]Sample Output[/align]

25.1327
3.1416
50.2655

题解：求自己和朋友可以分得的最大馅饼面积

#include<stdio.h>
#include<string.h>
#include<math.h>
#define MAX 10100
#define pi 3.1415926
double a[MAX];
int n,m;
int f(double x)
{
int i,s=0;
for(i=0;i<n;i++)
s+=(int)(a[i]/x);
return s;
}
int main()
{
int j,i,t;
double max,k;
scanf("%d",&t);
while(t--)
{
scanf("%d%d",&n,&m);
for(i=0;i<n;i++)
{
scanf("%lf",&k);
a[i]=k*k*pi;
}
double l=0,r=200000000000.0,mid;
while(r - l > 1e-6)
{
mid = (r + l)/2;
if(f(mid) >= m+1)//算上自己
l=mid;
else
r=mid;
}
printf("%.4lf\n",r);
}
return 0;
}