LeetCode知识点总结 - 933

LeetCode 933. Number of Recent Calls

题目

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.

思路

在添加新值的同时删掉最前面的值（如果在范围外的话）。

答案

class RecentCounter {

    LinkedList<Integer> slideWindow;

    public RecentCounter() {
        this.slideWindow = new LinkedList<Integer>();
    }

    public int ping(int t) {
        // step 1). append the current call
        this.slideWindow.addLast(t);

        // step 2). invalidate the outdated pings
        while (this.slideWindow.getFirst() < t - 3000)
            this.slideWindow.removeFirst();

        return this.slideWindow.size();
    }
}