二分朴素写法，简单易懂

#include<iostream>
#include<algorithm>
#include<cstring>
#include<cstdio>
using namespace std;
const int maxn = 1e5 + 5;
typedef long long ll;
int n;
int m;
double a[maxn];
signed main()
{
    cin >> n >> m;
    for (int i = 1; i <= n; i++) { cin >> a[i]; }
    double l = 0, r = 1e9;
    double mid = 0;
    while (l <= r)
    {
        mid = (l + r) / 2;
        ll temp = 0;
        for (int i = 1; i <= n; i++)temp += a[i] / mid;
        if (temp >= m)
            l = mid+0.001;
        else
            r = mid-0.001;
    }
    printf("%.2f", mid);
    return 0;
}