写的是卡时暴力，然后就过了。。。。。。

Code：

#include <bits/stdc++.h>
using namespace std;
int n, s, t, a[100005], qzh[100005];
double maxx = -0x7fffffff;
inline int sum(int l, int r)
{
    return qzh[r] - qzh[l - 1];
}
int main()
{
    cin >> n >> s >> t;
    for (register int i = 1; i <= n; i++)
        cin >> a[i];
    for (register int i = 1; i <= n; i++)
        qzh[i] = qzh[i - 1] + a[i];
    for (register int i = s; i <= t && (double)clock() / CLOCKS_PER_SEC <= 0.95; ++i)
        for (register int j = i; j <= n; ++j)
            maxx = max(maxx, sum(j - i + 1, j) / (1.0 * i));
    printf("%.3f", maxx);
}