359.Logger-Rate-Limiter

359. Logger Rate Limiter

题目地址

https://leetcode.com/problems/logger-rate-limiter/

题目描述

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;

代码

Approach #1 Queue + Set

Time: O(N) && Space: O(1)

class Pair<U, V> {
  public U first;
  public V second;

  public Pair(U first, V second) {
    this.first = first;
    this.second = second;
  }
}

class Logger {
    private LinkedList<Pair<String, Integer>> msgQueue;
  private HashSet<String> msgSet;

  /** Initialize your data structure here. */
  public Logger() {
        msgQueue = new LinkedList<String, Integer>>();
    msgSet = new HashSet<String>();
  }

  /** 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) {
        while (msgQueue.size() > 0) {
      Pair<String, Integer> head = msgQueue.getFirst();
      if (timestamp - head.second >= 10) {
        msgQueue.removeFirst();
        msgSet.remove(head.first);
      } else {
        break;
      }
    }

    if (!msgSet.contains(message)) {
      Pair<String, Integer> newEntry = new Pair<String, Integer>(message, timestamp);
      msgQueue.addLast(newEntry);
      msgSet.add(message);
      return true;
    } else {
      return false;
    }

  }
}

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

Approach #2 HashTable / Dictionary

class Logger {
  private HashMap<String, Integer> msgDict;

  public Logger() {
    msgDict = new HashMap<String, Integer>();
  }

  public boolean shouldPrintMessage(int timestamp, String message) {
    if (!this.msgDict.containsKey(message)) {
      this.msgDict.put(message, timestamp);
      return true;
    }

    Integer oldTimestamp = this.msgDict.get(message);
    if (timestamp = oldTimestamp >= 10) {
      this.msgDict.put(message, timestamp);
      return true;
    } else {
      return false;
    }
  }
}