LeetCode – Logger Rate Limiter

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Design a logger system that receive 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.

Example:

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;

Analysis

We can use HashTable to solve this problem. The key is the message, the value is the corresponding timestamp. For any message,

  1. if it is not in the HashTable, which means it is a new message, return true;
  2. if it is in the HashTable, which means it is an old message, we need to further check whether the old timestamp plus 10 is larger than the current time stamp. If it is larger, that means it has been printed in the past 10 seconds, return false;

Java solution