【杭电oj】1969 - Pie（二分）

点击打开题目 Pie

Time Limit: 5000/1000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others) Total Submission(s): 8851 Accepted Submission(s): 3225 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

   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

NWERC2006

题意：有 n 块蛋糕，分给 k+1 个人（加上本人），不能拼接，每个人得到的体积一样（圆柱体高为1，表面积一样即可）。问分的蛋糕最大为多少。

题解：从0 和表面积最大的那一块之间用二分，注意用 r - l 控制精度就行（1e-5才能AC）。

代码如下：

#include <cstdio>
#include <cmath>
#include <algorithm>
using namespace std;
#define PI acos(-1.0)
int n,k;
double pie[10000+11];
bool check(double t)
{
	int ant = 0;
	for (int i = 1 ; i <= n ; i++)
	{
		ant += (int)(pie[i] / t);
		if (ant >= k)
			return true;
	}
	return false;
}
int main()
{
	int u;
	double l,r,mid;
	scanf ("%d",&u);
	while (u--)
	{
		scanf ("%d %d",&n,&k);
		k++;		//加上本人 
		l = r = 0;
		for (int i = 1 ; i <= n ; i++)
		{
			scanf ("%lf",&pie[i]);
			pie[i] = pie[i] * pie[i] * PI;
			r = max (r , pie[i]);
		}
		while (r - l > 0.00001)		//控制精度（大十倍就会WA） 
		{
			mid = (l + r) / 2.0;
			if (check(mid))
				l = mid;
			else
				r = mid;
		}
		printf ("%.4lf\n",l);
	}
	return 0;
}