You have a `RecentCounter` class which counts the number of recent requests within a certain time frame.

Implement the `RecentCounter` class:

- `RecentCounter()` Initializes the counter with zero recent requests.
- `int ping(int t)` Adds a new request at time `t`, where `t` represents some time in milliseconds, and returns the number of requests that has happened in the past `3000` milliseconds (including the new request). Specifically, return the number of requests that have happened in the inclusive range `[t - 3000, t]`.

It is guaranteed that every call to `ping` uses a strictly larger value of `t` than the previous call.

Example 1:

    Input
    ["RecentCounter", "ping", "ping", "ping", "ping"]
    [[], [1], [100], [3001], [3002]]
    Output
    [null, 1, 2, 3, 3]

    Explanation
    RecentCounter recentCounter = new RecentCounter();
    recentCounter.ping(1);     // requests = [1], range is [-2999,1], return 1
    recentCounter.ping(100);   // requests = [1, 100], range is [-2900,100], return 2
    recentCounter.ping(3001);  // requests = [1, 100, 3001], range is [1,3001], return 3
    recentCounter.ping(3002);  // requests = [1, 100, 3001, 3002], range is [2,3002], return 3

Constraints:

- `1 <= t <= 109`
- Each test case will call `ping` with strictly increasing values of `t`.
- At most `104` calls will be made to `ping`.