leetcode362

Design a hit counter which counts the number of hits received in the past 5 minutes.
Each function accepts a timestamp parameter (in seconds granularity) and you may assume that calls are being made to the system in chronological order (ie, the timestamp is monotonically increasing). You may assume that the earliest timestamp starts at 1.
It is possible that several hits arrive roughly at the same time.

1.普通情况：Queue. 在每一秒数据不多时。
hit：q.push(time)
Get: 对q的peek一个个看过去，如果超时了就poll掉，最后hit数就是q.size()

2.follow up: Array[300]. 在每一秒数据很多的情况，scale。
Hit: %后存入。如果那个位置不是当前时间的，就用1取代，如果是当前时间，就加上去。
Get: 统计所有有效时间的部分。O(300)稳定下来了。不是很小，但这样也总比一秒来5000条那你get一次要删5000条的O(5000)好啊。

实现1. Queue：

class HitCounter {

    private Queue<Integer> q;
    /** Initialize your data structure here. */
    public HitCounter() {
        this. q = new LinkedList<>();
    }
    
    /** Record a hit.
        @param timestamp - The current timestamp (in seconds granularity). */
    public void hit(int timestamp) {
        q.offer(timestamp);
    }
    
    /** Return the number of hits in the past 5 minutes.
        @param timestamp - The current timestamp (in seconds granularity). */
    public int getHits(int timestamp) {
        while (!q.isEmpty() && q.peek() + 300 <= timestamp) {
            q.poll();
        }
        return q.size();
    }
}

/**
 * Your HitCounter object will be instantiated and called as such:
 * HitCounter obj = new HitCounter();
 * obj.hit(timestamp);
 * int param_2 = obj.getHits(timestamp);
 */

实现2. Array. scale：

class HitCounter {
    
    private int[] cnt;
    private int[] time;
    /** Initialize your data structure here. */
    public HitCounter() {
        cnt = new int[300];
        time = new int[300];
    }
    
    /** Record a hit.
        @param timestamp - The current timestamp (in seconds granularity). */
    public void hit(int timestamp) {
        if (time[timestamp % 300] == timestamp) {
            cnt[timestamp % 300]++;
        } else {
            time[timestamp % 300] = timestamp;
            cnt[timestamp % 300] = 1;
        }
    }
    
    /** Return the number of hits in the past 5 minutes.
        @param timestamp - The current timestamp (in seconds granularity). */
    public int getHits(int timestamp) {
        int ans = 0;
        for (int i = 0; i < 300; i++) {
            if (time[i] + 300 > timestamp) {
                ans += cnt[i];
            }
        }
        return ans;
    }
}

/**
 * Your HitCounter object will be instantiated and called as such:
 * HitCounter obj = new HitCounter();
 * obj.hit(timestamp);
 * int param_2 = obj.getHits(timestamp);
 */