POJ 3122 - Pie(二分)

Pie
Time Limit: 1000MS Memory Limit: 65536K
Total Submissions: 15626 Accepted: 5339 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

题意:
给出N个派,F个好友,你要和好友们共同分派.每个人只能从一个派里面拿一部分.
要求每个人拿的一样多,问最多能拿多少.

解题思路:
二分.每个人只能从一个派里面拿,那么看就每个派的大小除以当前的平均数,如果商的和大于,总人数,就找更大的平均数,反之找小的.

AC代码:

#include<stdio.h>#include<math.h>const int maxn = 10005;double qdu[maxn];int n;int f;bool isGood(double x){    int cnt = 0;    for(int i = 0;i < n;i++)    cnt += (int)(qdu[i]/x);    if(cnt >= f)    return 1;    return 0;}int main(){    int loop;    scanf("%d",&loop);    while(loop--)    {        scanf("%d%d",&n,&f);        f++;        double sum = 0;        for(int i = 0;i < n;i++)    scanf("%lf",&qdu[i]),qdu[i] *= qdu[i]*M_PI,sum += qdu[i];        double left = 0;        double right = sum/f;        double mid;        while((right-left) > 1e-6)        {            mid = (right+left)/2;            if(isGood(mid)) left = mid;            else            right = mid;        }        printf("%.4f\n",mid);    }    return 0;}