代码如下，一直卡3个测试点

#include<iostream>
#include<algorithm>

using namespace std;

const int N = 1e5 + 10;

double a[N], b[N], q[N];
int n, m;

int main()
{
    cin >> n >> m;
    for(int i = 1; i <= n; i++) 
    {
        cin >> a[i];
        a[i] += a[i - 1];
    }

    int cnt = 0;
    for(int i = 1; i <= n - m + 1; i++)
        b[cnt++] = (a[i + m - 1] - a[i - 1]) / m * 1000;

    int len = 0;
    for(int i = 0; i < cnt; i++)
    {
        int l = 0, r = len;
        while(l < r)
        {
            int mid = l + r + 1 >> 1;
            if(q[mid] < b[i]) l = mid;
            else r = mid - 1;
        }
        q[r + 1] = max(q[r + 1], b[i]);
        len = max(len, r + 1);
    }
    cout << (long long)q[len] << endl;

    return 0;
}