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How to implement the standard Queue ADT?

Posted on 2008-06-16
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Last Modified: 2009-05-23
Hello.
I have to show how to implement the standard Queue ADT using only a Priority Queue and one additional integer instance variable. Can anyone provide a text description of the process?
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Question by:secondcup
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8 Comments
 
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Expert Comment

by:Infinity08
ID: 21795843
Is this an assignment ? How far did you get ? What are you unsure about ?
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Author Comment

by:secondcup
ID: 21796786
I have no idea how to implement the Queue ADT using only a Priority Queue and one additional integer instance variable.  I just know we can implement it by using List...but I do not get what it means by one additional integer..
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Accepted Solution

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Infinity08 earned 168 total points
ID: 21796980
A queue is a special case of a priority queue, where the priority is basically the time of insertion.
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Assisted Solution

by:Sankozi
Sankozi earned 166 total points
ID: 21797194
I think this is good solution. You just need this additional integer to determine priority of next element that will be pushed.

class Queue
{
  PQueue pQueue = new PQueue(); 
  int nextPriority = Integer.MAX_VALUE;
 
  void push(T t)
  {
    pQueue.insertWithPriority(t, nextPriority --);
 
    if(nextPriority == Integer.MIN_VALUE)
    {
      reload(); //"restart" queue
    }
  }
 
  T pop()
  {
    p.getNext();
  }
 
  void reload()
  {
    oldPQ = pQueue;
    pQueue = new PQueue();
    nextPriority = Integer.MAX_VALUE;
 
    while(!oldPQ.empty())
    {
      push(oldPQ.pop());
    }
  }
}

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Expert Comment

by:Infinity08
ID: 21797260
Sankozi, be careful with posting full code solutions to what might be an assignment - that's not permitted on this site.
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Assisted Solution

by:CCSINCOMETRUST
CCSINCOMETRUST earned 166 total points
ID: 21917134
You may want to consider implementing a circular queue depending on what it will be used for and if you don't know how much it will hold ahead of time.

Hint: Google "Java Circular Queue" or "C++ Circular Queue" - you should have no problem finding code that you can use.
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