样例过了，用的二分+单调队列check， chk 函数用来验证 mid 的值是否正确。

不是 freopen 的问题，本贴提到的所有提交结果均为去掉 freopen 后的提交结果。

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
ll n;
ll s, t;
ll a[100001];
double tmp[100001];
double sum[100001];
bool chk(double x)
{
	for(int i = 1; i <= n; i++)
		tmp[i] = a[i] - x, sum[i] = sum[i - 1] + tmp[i];
	deque <ll> q;
	for(int i = s; i <= n; i++)
	{
		while(q.size() && sum[q.back()] - sum[i - s] <= 1e-6)
			q.pop_back();
		q.push_back(i - s);
		if(q.size() && i - q.front() > t)
			q.pop_front();
		if(q.size() && sum[i] - sum[q.front()] >= 0)
			return 1;
	}
	return 0;
}
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);     cout.tie(0);
	freopen("P1419.in", "r", stdin);
	cin >> n >> s >> t;
	for(int i = 1; i <= n; i++)
		cin >> a[i];
	double l = -1e4, r = 1e4, ans;
	while(r - l > 1e-6)
	{
		double mid = (l + r) / 2;
		if(chk(mid))
			l = mid + 0.00001, ans = mid;
		else
			r = mid - 0.00001;
	}
	cout << setprecision(3) << fixed << ans;
	return 0;
}