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# Priority queue

, 28 Mar 2004
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Another addition to the System.Collections namespace - a priority queue, also known as a heap.

## Introduction

Many algorithms - for instance Dijkstra's well-known search for the shortest path - run most efficient with a 'semi-sorted' list, which always has the smallest element up front. The most efficient structure for this purpose is a heap, also called priority queue.

## Usage

The `PriorityQueue` class is built in the guidelines of the `System.Collections` namespace. Comparison is done through the `IComparer` interface, or, if none is specified, through the `IComparable` implementation of the provided objects. The objects in the PQ need not have all the same type but they have to be comparable with each other.

Next to the standard `System.Collections` methods (`Count`, `Contains`, ... you name it), the PQ supports 3 main operations:

• `Push()`: This will add an object to the PQ, reforming the structure so that this element is at the front if it is the currently smallest. The complexity of the operation is O(ld n).
• `Pop()`: This will remove and return the current head of the PQ, which always is the smallest element. Complexity O(ld n).
• `Update()`: It might be necessary to change elements that are already in the queue. Because this is not very common (you need to find the element first), it can only be done by the explicit `IList` implementation (the indexer should not be used in any other case). Once you set the indexer, the PQ will automatically reorder. Complexity O(ld n) (surprise;))

## Example

```/// We create a PQ, add some random numbers and retreive them in sorted order:

IPriorityQueue PQ = new BinaryPriorityQueue();
Random R = new Random();
int i;
for(i=0;i<50;i++)
{
PQ.Push(R.Next(1000));
}
while(PQ.Count>0)
Console.WriteLine(PQ.Pop());```

## History

• 30.3.04 - Inserted.
• 31.3.04 - renamed the main class to `BinaryPriorityQueue`.

Created `IPriorityQueue` interface.

A list of licenses authors might use can be found here

## Share

 Software Developer (Senior) Germany
I did my diploma in Dresden and Sydney where I dealt with algorithms, agents and other cool AI stuff. Now I moved to Frankfurt to work on my PhD dealing with software structures for artificial intelligence systems. If I can, I do things in C# and ASP.NET, but if I have to, my C++, Java and SQL are not that bad.
Long Live .NET.

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 Thanks a lot majdaldin122-Apr-11 2:59 majdaldin1 22-Apr-11 2:59
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 My vote of 4 s.hamed_rezvani12-Jan-11 3:48 s.hamed_rezvani 12-Jan-11 3:48
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 implemntinig priority Quesues Member 331791728-Aug-08 7:42 Member 3317917 28-Aug-08 7:42
 hi ! i am implemnting a program that first * make Queue_Adt * create a program structure 1. Create a program structure. It contains a float ProgramAge (or creationTime), and two imtegers programNumber and priority_level. ProgramNumber is a just like a counter. Program age can have values 0 low, high and mid. 3. Create a function program getNextProgram(), that creates a program, randomly assigns values to its programAge and priority_level (0,1 or 2) and returns the program. It also assigns value to programNumber. let programNumber = 0 for first program, programNumber=1 for second and so on. 4. Get a program from getNextProgram(). Based on the priority of the program, select the queue for the program. 5. Once the queue is decided, insert the program into the queue depending on its ProgramAge. The program with the highest ProgramAge should be in front of the queue. 6. Repeat 4-5, 20 times. 7. Write the configuration of each queue into file. For example file should look something like: High: ProgramNumber = 2, ProgramAge=3.5 ProgramNumber = 4, ProgramAge=2 … Mid: ProgramNumber = 0, ProgramAge=13.2 … Low: ProgramNumber = 3, ProgramAge=4.0 ProgramNumber = 1, ProgramAge=3.0 … but stuck in step " 5 " also help me out how to put that data on text file : sample code of main class is given ``` #include #include #include "Queue.cpp" #include // For time()     class Programm{ private: int prior_level,program_no; float creation_time; public: Programm(){   program_no=0; }   void set_id() { program_no++; } void set_time() { //srand(time(0)); creation_time=(rand() % 20) + 1; } void set_prior() { prior_level=(rand() % 3) ; }   int get_id() { return program_no; } float get_time() { return creation_time;   } int get_prior() { return prior_level; }   };//class void main()   {     Queue low,high,medium; Programm p; int pl,hl,ml=0;   for (int i=0;i<=20;i++) { p.set_prior(); if(p.get_prior()==0) {     low.enQueue(p);   cout<<"the no of element in low ="<
 implemntinig priority Quesues Member 331791728-Aug-08 7:35 Member 3317917 28-Aug-08 7:35
 Fast Priority Queue Implementation of Dijkstra Shortest Path Algorithm Tolga Birdal31-Mar-08 5:38 Tolga Birdal 31-Mar-08 5:38
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 Your PriorityQueue code converted to Visual Basic Enigmativity30-Mar-04 22:51 Enigmativity 30-Mar-04 22:51
 Re: Your PriorityQueue code converted to Visual Basic BenDi31-Mar-04 0:14 BenDi 31-Mar-04 0:14
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 Re: Care to join a "all collection" project ? Jonathan de Halleux30-Mar-04 2:31 Jonathan de Halleux 30-Mar-04 2:31
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 Re: Care to join a "all collection" project ? Jonathan de Halleux30-Mar-04 3:27 Jonathan de Halleux 30-Mar-04 3:27
 Re: Care to join a "all collection" project ? BenDi2-Apr-04 22:45 BenDi 2-Apr-04 22:45
 Re: Care to join a "all collection" project ? Jonathan de Halleux3-Apr-04 0:41 Jonathan de Halleux 3-Apr-04 0:41
 Re: Care to join a "all collection" project ? Jonathan de Halleux3-Apr-04 7:51 Jonathan de Halleux 3-Apr-04 7:51
 Re: Care to join a "all collection" project ? Jonathan de Halleux2-Apr-04 3:46 Jonathan de Halleux 2-Apr-04 3:46
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 Re: Which heap ? Jonathan de Halleux30-Mar-04 3:00 Jonathan de Halleux 30-Mar-04 3:00
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