题目描述：

LeetCode 635. Design Log Storage System

You are given several logs that each log contains a unique id and timestamp. Timestamp is a string that has the following format: Year:Month:Day:Hour:Minute:Second, for example, 2017:01:01:23:59:59. All domains are zero-padded decimal numbers.

Design a log storage system to implement the following functions:

void Put(int id, string timestamp): Given a log's unique id and timestamp, store the log in your storage system.

int[] Retrieve(String start, String end, String granularity): Return the id of logs whose timestamps are within the range from start to end. Start and end all have the same format as timestamp. However, granularity means the time level for consideration. For example, start = "2017:01:01:23:59:59", end = "2017:01:02:23:59:59", granularity = "Day", it means that we need to find the logs within the range from Jan. 1st 2017 to Jan. 2nd 2017.

Example 1:

put(1, "2017:01:01:23:59:59");
put(2, "2017:01:01:22:59:59");
put(3, "2016:01:01:00:00:00");
retrieve("2016:01:01:01:01:01","2017:01:01:23:00:00","Year"); // return [1,2,3], because you need to return all logs within 2016 and 2017.
retrieve("2016:01:01:01:01:01","2017:01:01:23:00:00","Hour"); // return [1,2], because you need to return all logs start from 2016:01:01:01 to 2017:01:01:23, where log 3 is left outside the range.

Note:

1. There will be at most 300 operations of Put or Retrieve.
2. Year ranges from [2000,2017]. Hour ranges from [00,23].
3. Output for Retrieve has no order required.

题目大意：

给定以二元组(id, 时间戳)表示的日志，时间戳格式为Year:Month:Day:Hour:Minute:Second

设计系统支持日志存储，并支持在年，月，日，时，分，秒粒度时间范围内查询日志ID列表

解题思路：

字典（Map）

日志利用数据结构Map<String, Integer>进行存储

其中key为时间粒度，value为日志ID列表

执行retrieve操作时，根据时间粒度对时间戳进行截取

Java代码：

public class LogSystem {

    private HashMap<String, Integer> dmap = new HashMap<>();
    private final String[] gras = "Year:Month:Day:Hour:Minute".split(":");
    private final int[] ends = {4, 7, 10, 13, 16};
    
    private String getKeyByGra(String timestamp, String gra) {
        for (int i = 0; i < gras.length; i++) {
            if (gra.equals(gras[i])) {
                return timestamp.substring(0, ends[i]);
            }
        }
        return timestamp;
    }
    
    public LogSystem() {
    }
    
    public void put(int id, String timestamp) {
        dmap.put(timestamp, id);
    }
    
    public List<Integer> retrieve(String s, String e, String gra) {
        String sk = getKeyByGra(s, gra);
        String ek = getKeyByGra(e, gra);
        List<Integer> ans = new LinkedList<>();
        for (String key : dmap.keySet()) {
            String ck = getKeyByGra(key, gra);
            if (sk.compareTo(ck) <= 0 && ck.compareTo(ek) <= 0) {
                ans.add(dmap.get(key));
            }
        }
        return ans;
    }

}

/**
 * Your LogSystem object will be instantiated and called as such:
 * LogSystem obj = new LogSystem();
 * obj.put(id,timestamp);
 * List<Integer> param_2 = obj.retrieve(s,e,gra);
 */

 

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