LeetCode-Number of Recent Calls

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Description：
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:

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

题意：编写几个类，计算返回ping(t)，其含义是计算所有在[t-3000, t]范围内的ping的次数；

解法：既然只要求计数[t-3000, t]范围内的ping的次数，并且每次t都会比之前的来的大，那么我们可以利用一个队列来实现这个计算，对于每次需要ping的一个新的t添加到队尾，并且将队列从首部开始移除所有不满足[t-3000, t]范围内的ping；那么最终返回的队列的长度就是我们所要求得在范围[t-3000, t]内的ping的次数了；

Java

class RecentCounter {
    Deque<Integer> call;
    public RecentCounter() {
        call = new ArrayDeque<Integer>();
    }
    
    public int ping(int t) {
        if (call.isEmpty()) {
            if (t == 0) return 0;
            call.addLast(t);
            return 1;
        }
        while (!call.isEmpty() && t - 3000 > call.getFirst()) call.removeFirst();
        call.addLast(t);
        return call.size();
    }
}

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