DZone Snippets: queue code

Using a Stack with Ruby

jrobertson (James Robertson) — Sun, 24 Aug 2008 22:06:43 GMT

Source: Mac Developer Tips » Using a Stack with Ruby [macdevelopertips.com]

... creating a simple Stack class as follows:

class Stack



  def initialize

   @the_stack = []

  end



  def push(item)

    @the_stack.push item

  end



  def pop

    @the_stack.pop

  end



  def count

    @the_stack.length

  end

end

Here is how you might use the stack:

  stack = Stack.new

  stack.push('abc')

  stack.push(100)

  stack.count

  stack.pop()

If need be, you could also add a few convenience methods such as clearing the stack or looking at the last element (without popping it off the stack):

  def clear

    @the_stack.clear

  end



  def look

    @the_stack.last

  end

Instruct a shared whiteboard to save and refresh

jrobertson (James Robertson) — Thu, 27 Mar 2008 19:14:07 GMT

The following code used with the ProjectX API informs the client web browser that the whiteboard will be refreshed in 5 seconds. It then archives the current whiteboard information, formats it, and sends a message to each web browser to refresh their view.





  

    

      

        ecmascript

        startRefresh(5)

        system

      

    

    

      

        5

      

    

    

      

    

    

      

        ecmascript

        reloadDocument()

        system

*update 1:14am*
The whiteboard demo [rorbuilder.info] allows the user to draw using the mouse within the web browser which renders SVG. Tested on Flock and Firefox.

*update 4:42pm 28 Mar 08*
You can also view the whiteboard message queue [rorbuilder.info].

*update 6:29pm Mar 08*
I've created a short url (http://rubyurl.com/vxHD) (to demonstrate the cleaning of the whiteboard) which redirects to this http://rorbuilder.info/api/projectx.cgi?xml_project=ecmascriptstartRefresh(5)system5ecmascriptreloadDocument()system

I've

a silly FIFO in Erlang (you should use OTP's queue.erl instead)

ayrnieu (Julian Fondren) — Sun, 01 Oct 2006 09:36:56 GMT



-module(fifo).

-export([new/0, loop/0, push/2, pop/1]).



new() ->

    spawn(?MODULE, loop, []).



loop() ->

    receive

        {Pid,pop} ->

            Pid ! {self(),receive {push,X} ->

                                  X

                          end),

            loop()

    end.



push(Fifo,X) ->

    Fifo ! {push,X},

    X.



pop(Fifo) ->

    Fifo ! {self(),pop},

    receive {Fifo,X} ->

            X

    end.

priority-queue functions

gregg.irwin (Gregg Irwin) — Fri, 13 Jan 2006 04:00:13 GMT



REBOL [

    Title: "Cheasy (Cheap-n-Easy) Priority Queue"

]



pq-insert: func [

    list [any-block!]   "The queue"

    item

    priority [integer!]

][

    sort/skip/reverse append list reduce [priority item] 2

]



pq-remove: func [

    "Remove an item from the priority queue"

    list [any-block!]   "The queue"

    /index  "Remove a specific item"

        idx [integer!] "The specific item to remove"

][

    remove/part either index [at list (idx * 2 - 1)][head list] 2

]



pq-first: func [

    list [any-block!]   "The queue"

][

    ; skip over the priority value and return the actual value

    ; that was inserted in the queue.

    first next head list

]



priority-queue: make object! [

    data: copy []



    insert: func [item priority] [pq-insert data item priority]



    remove: func [/index idx] [

        either index [pq-remove/index data idx][pq-remove data]

    ]



    first: does [pq-first data]

]







pq: copy []

print pq-insert pq "A" 1

print pq-insert pq "B" 10

print pq-insert pq "C" 100

print pq-insert pq "D" 1000

print pq-remove/index pq 3

print pq-remove pq

print mold pq

print pq-insert pq "CC" 100

print pq-insert pq "CCC" 100

print pq-insert pq "D" 1000

print pq-insert pq "CCCC" 100

print pq-insert pq "CCCCC" 100

print pq-remove pq

print pq-insert pq "CCCCCC" 100

print pq-insert pq "CCCCCCC" 100



print ""



pq: make priority-queue []

print pq/insert"A" 1

print pq/insert"B" 10

print pq/insert"C" 100

print pq/insert"D" 1000

print pq/remove/index 3

print pq/remove ;pq

print mold pq/data

print pq/insert"CC" 100

print pq/insert"CCC" 100

print pq/insert"D" 1000

print pq/insert"CCCC" 100

print pq/insert"CCCCC" 100

print pq/remove ;pq/data

print pq/insert"CCCCCC" 100

print pq/insert"CCCCCCC" 100





halt

Priority Queue

korakot (Korakot Chaovavanich) — Fri, 16 Sep 2005 19:55:01 GMT



pq = PriorityQueue()



pq.put(('b', 1))

pq.put(('a', 1))

pq.put(('c', 1))

pq.put(('z', 0))

pq.put(('d', 2))



while not pq.empty():

  print pq.get(),   

# z b a c d

Get the implementation of Priority Queue here.