C#LeetCode刷题之#933-最近的请求次数（Number of Recent Calls）

问题

写一个 RecentCounter 类来计算最近的请求。

它只有一个方法：ping(int t)，其中 t 代表以毫秒为单位的某个时间。

返回从 3000 毫秒前到现在的 ping 数。

任何处于 [t – 3000, t] 时间范围之内的 ping 都将会被计算在内，包括当前（指 t 时刻）的 ping。

保证每次对 ping 的调用都使用比之前更大的 t 值。

输入：inputs = [“RecentCounter”,”ping”,”ping”,”ping”,”ping”], inputs = [[],[1],[100],[3001],[3002]]

输出：[null,1,2,3,3]

提示：

• 每个测试用例最多调用 10000 次 ping。
• 每个测试用例会使用严格递增的 t 值来调用 ping。
• 每次调用 ping 都有 1 <= t <= 10^9。

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.

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.

示例

public class Program {

    public static void Main(string[] args) {
        var count = new RecentCounter();

        Console.WriteLine(count.Ping(1));
        Console.WriteLine(count.Ping(100));
        Console.WriteLine(count.Ping(3001));
        Console.WriteLine(count.Ping(3002));

        Console.WriteLine();

        var count2 = new RecentCounter2();

        Console.WriteLine(count2.Ping(1));
        Console.WriteLine(count2.Ping(100));
        Console.WriteLine(count2.Ping(3000));
        Console.WriteLine(count2.Ping(5000));

        Console.ReadKey();
    }

    public class RecentCounter {

        public RecentCounter() {
            _list = new List<int>();
        }

        private List<int> _list = null;

        public int Ping(int t) {
            //列表法，思路简单暴力
            _list.Add(t);
            var last = _list[_list.Count - 1];
            var count = 1;
            for(var i = _list.Count - 2; i >= 0; i--) {
                if(last - _list[i] <= 3000) {
                    count++;
                } else {
                    break;
                }
            }
            return count;
        }

    }

    public class RecentCounter2 {

        public RecentCounter2() {
            _queue = new Queue<int>();
        }

        private Queue<int> _queue = null;

        public int Ping(int t) {
            //队列法
            _queue.Enqueue(t);
            //干掉时间差大于 3000 的，它们没有必要参与运算
            while(t - _queue.Peek() > 3000) _queue.Dequeue();
            return _queue.Count;
        }

    }

}

以上给出2种算法实现，以下是这个案例的输出结果：

1
2
3
3

1
2
3
2

分析：

显而易见，以上2种算法的时间复杂度均为： ​ 。