Logger Rate Limiter Solution (LeetCode)

This question is from the LeetCode Challenge (Aug-2020). See the original question here

Design a logger system that receive a stream of messages along with its timestamps, each message should be printed if and only if it is not printed in the last 10 seconds.

Given a message and a timestamp (in seconds granularity), return true if the message should be printed in the given timestamp, otherwise returns false.

It is possible that several messages arrive roughly at the same time.

Logger logger = new Logger();

// logging string "foo" at timestamp 1
logger.shouldPrintMessage(1, "foo"); returns true; 

// logging string "bar" at timestamp 2
logger.shouldPrintMessage(2,"bar"); returns true;

// logging string "foo" at timestamp 3
logger.shouldPrintMessage(3,"foo"); returns false;

// logging string "bar" at timestamp 8
logger.shouldPrintMessage(8,"bar"); returns false;

// logging string "foo" at timestamp 10
logger.shouldPrintMessage(10,"foo"); returns false;

// logging string "foo" at timestamp 11
logger.shouldPrintMessage(11,"foo"); returns true;

The template of the solution (Logger class) should have the following APIs.

class Logger {
  
  HashMap<String, Integer> hash;
  
  /** Initialize your data structure here. */
  public Logger() {
    hash = new HashMap<String, Integer>();
  }
  
  /** Returns true if the message should be printed in the given timestamp, otherwise returns false.
    If this method returns false, the message will not be printed.
    The timestamp is in seconds granularity. */
  public boolean shouldPrintMessage(int timestamp, String message) {
    Integer prevTime = hash.get(message);
    if(prevTime == null || (timestamp - prevTime >= 10) )
    {
      hash.put(message, timestamp);
      return true;
    }
    return false;
  }
}

/**
 * Your Logger object will be instantiated and called as such:
 * Logger obj = new Logger();
 * boolean param_1 = obj.shouldPrintMessage(timestamp,message);
 */

Solution:

For each of the string that the Logger file receives, it need to keep a track of the last time this string was logged. This log-time is an integer value. So, we need to store one integer value for each of the string that we are receiving. A HashMap is a good data structure to store a <key, value> pair.

Following is the solution for the given question:

class Logger {
  
  HashMap<String, Integer> hash;
  
  /** Initialize your data structure here. */
  public Logger() {
    hash = new HashMap<String, Integer>();
  }
  
  /** Returns true if the message should be printed in the given timestamp, otherwise returns false.
    If this method returns false, the message will not be printed.
    The timestamp is in seconds granularity. */
  public boolean shouldPrintMessage(int timestamp, String message) {
    Integer prevTime = hash.get(message);
    if(prevTime == null || (timestamp - prevTime >= 10) )
    {
      hash.put(message, timestamp);
      return true;
    }
    return false;
  }
}

The time complexity of shouldPrintMessage function is constant.