poj 3122 Pie

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.

高精度的题感觉就有点玄学ac，之前遇到过把%.4lf改成%.4f就过了的，这次也是一样

====回到正题

这题就是二分，只不过变成了浮点数的二分，所以注意精度的处理

// #include <bits/stdc++.h>
#include <iostream>
#include <complex>
#include <cstdio>
#include <algorithm>
using namespace std;
typedef long long LL;


const double pi = atan(1)*4;
int n,f;
double maxr;
double pie[10005];


bool oks(double r2){
  int total = 0;
  for (int i=1;i<=n;i++){
    // if (r2 - 16 <= fabs(0.00001)){
    //   cout << "HERE" << pie[i]/r2 << " " << (int)(pie[i] / r2) << endl;
    // }
    total += (int)(pie[i] / r2);
  }
  if (total >= f+1){
    return true;
  }
  return false;
}

double search(double l,double r){
  if (r-l <= fabs(0.000001)){
    return (l + r) / 2;
  }
  double mid = l + (r - l) / 2;
  if (oks(mid)){
    return search(mid,r);
  }
  else
    return search(l,mid);
}
int main()
{
  // freopen("test.in","r",stdin);
  int T;
  scanf("%d",&T);
  for (int times = 1; times <= T; times ++){
    maxr = 0;
    scanf("%d %d",&n,&f);
    for (int i=1;i<=n;i++){
      scanf("%lf",&pie[i]);
      pie[i] = pie[i] * pie[i];
      maxr = max(maxr,pie[i]);
    }
    double ans = search(0,maxr);
    // cout << ans << " ";
    printf("%.4f
",ans*pi);
  }
    return 0;
}