Description,
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;

Doubly LinkedList + HashMap solutions

Algorithm:
If we use only hashmap to store the <’log message’, ‘timestamp’> pair, the hashmap will grow very large if we expect a lot of new logs over time.
The solution below used a doubly LinkedList to record the sequence of incoming logging request, and will removing older log records from hashmap.

class DoubledLL(object):
    def __init__(self, val, message):
        """
        Doubled LinkedList
        """
        self.prev = None
        self.next = None
        self.val = val
        self.message = message

class Logger(object):

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.hm = dict()
        self.head = DoubledLL(0, 'HEAD')
        self.tail = DoubledLL(0, 'TAIL')
        self.head.next = self.tail
        self.tail.prev = self.head
        
    def shouldPrintMessage(self, timestamp, message):
        """
        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.
        :type timestamp: int
        :type message: str
        :rtype: bool
        """

        if message not in self.hm:
            self._updateHMappendNodeToTail(message, timestamp)
            return True # logging it
        else:
            existingNode = self.hm.get(message)
            timestampToCut = existingNode.val
            if timestamp - timestampToCut >= 10:
                self._setNewHeadandCleanHM(existingNode)
                self._updateHMappendNodeToTail(message, timestamp)
                return True
            else:
                return False

                
    def _updateHMappendNodeToTail(self, message, timestamp): 
        newNode = DoubledLL(timestamp, message)
        self.hm[message] = newNode
        
        #adding node to the tail
        self.tail.prev.next = newNode
        newNode.prev = self.tail.prev
        self.tail.prev = newNode
        newNode.next = self.tail

    
    def _setNewHeadandCleanHM(self, existingNode):
        #remove all node before it from the hashmap
        cur = self.head.next
        while cur != existingNode:
            self.hm.pop(cur.message)
            cur = cur.next
        
        # GC will clean the nodes before it
        self.head.next = existingNode.next
        existingNode.next.prev = self.head
        
        


# Your Logger object will be instantiated and called as such:
# obj = Logger()
# param_1 = obj.shouldPrintMessage(timestamp,message)

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