求解释，求原理啊！

#include <iostream>
#include <cstdio>

#define ll long long

using namespace std;

const int N=1e4+5;
const double eps=1e-9;
const int inf=1e9;

int len[N];

int max(int a,int b){  return a>b?a:b; }

int main()
{
	//freopen("in.in","r",stdin);
	int n,k,ans;
	double tmp;
	while(~scanf("%d%d",&n,&k))
	{
		int l=0,r,mid;
		for(int i=0;i<n;i++)
		{
			cin>>tmp;
			//scanf("%lf",&tmp);
			len[i]=(int)(tmp*100+eps);
			r=max(r,len[i]);
		}
		ans=0;
		while(l<=r)
		{
			mid=(l+r)/2;
			int sum=0;
			if(mid==0) sum=inf;
			else for(int i=0;i<n;sum+=len[i]/mid,i++);
			if(sum>=k)
			{
				ans=max(ans,mid);
				l=mid+1;
			}
			else
				r=mid-1;
		}
		printf("%.2lf\n",ans*0.01);
	}
	return 0;
}