[LeetCode] 359. Logger Rate Limiter

Problem

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;

Solution #1: map saving earliest good time

class Logger {

    Map<String, Integer> shouldPrintMap;
    /** Initialize your data structure here. */
    public Logger() {
        shouldPrintMap = new HashMap<>();
    }
    
    /** 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) {
        int goodTime = shouldPrintMap.getOrDefault(message, 0);
        if (timestamp < goodTime) return false;
        shouldPrintMap.put(message, timestamp+10);
        return true;
    }
}

Solution #2: remove obsolete messages by using a queue and a set

class Logger {
    class Log {
        int time;
        String message;
        public Log(int t, String m) {
            this.time = t;
            this.message = m;
        }
    }
    
    Queue<Log> queue;
    Set<String> set;
    public Logger() {
        queue = new LinkedList<>();
        set = new HashSet<>();
    }

    public boolean shouldPrintMessage(int timestamp, String message) {
        //remove recent messages in last 10 sec from both queue and set
        while (!queue.isEmpty() && queue.peek().time <= timestamp-10) {
            Log recentLog = queue.poll();
            set.remove(recentLog.message);
        }
        if (!set.contains(message)) {
            queue.offer(new Log(timestamp, message));
            set.add(message);
            return true;
        }
        return false;
    }
}