P1577 切绳子

​​传送门​​

思路：

用二分对答案mid进行枚举，若按照当前mid进行切割可获得的长度大于k，则l = mid+0.0001，否则r = mid-0.0001，最后用floor向下取整；

#include<bits/stdc++.h>
using namespace std;
#define ll long long
double a[1000010];
int n,m;
bool check(double x)
{
  int cnt = 0;
  for(int i = 1; i <= n; i++)
  {
    cnt += (a[i] / x);
  }
  return cnt >= m;
}
int  main()
{
  cin>>n>>m;
  for(int i = 1; i <= n; i++)
  {
    cin>>a[i];
  }
  double l = 0.0,r = 100010.0;
  while(l-r<0.0001)
  {
    double mid = (l+r)/2;
    if(check(mid))
    {
      l = mid+0.0001;
    }
    else
    {
      r = mid-0.0001;
    }
  }
  printf("%0.2lf\n",floor(l*100)*1.0/100.0);
}