Number of Recent Calls

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Write a class RecentCounter to count recent requests.

It has only one method: ping(int t), where t represents some time in milliseconds.

Return the number of pings that have been made from 3000 milliseconds ago until now.

Any ping with time in [t - 3000, t] will count, including the current ping.

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

Example 1:

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

Note:

1. Each test case will have at most 10000 calls to ping.
2. Each test case will call ping with strictly increasing values of t.
3. Each call to ping will have 1 <= t <= 10^9.

思路：就是一个queue，注意pop出来之后要check是否为空；

class RecentCounter {

    LinkedList<Integer> queue;
    
    public RecentCounter() {
        this.queue = new LinkedList<Integer>();
    }
    
    public int ping(int t) {
        if(queue.size() == 0) {
            queue.add(t);
            return queue.size();
        } else if(t - queue.peek() <= 3000) {
            queue.add(t);
            return queue.size();
        } else {
            // pop until number < 3000;
            while(!queue.isEmpty() && (t - queue.peek() > 3000)) {
                queue.pop();
            }
            queue.add(t);
            return queue.size();
        }
    }
}

/**
 * Your RecentCounter object will be instantiated and called as such:
 * RecentCounter obj = new RecentCounter();
 * int param_1 = obj.ping(t);
 */