Class: Containers::PriorityQueue

Inherits:
Object
  • Object
show all
Includes:
Enumerable
Defined in:
lib/containers/priority_queue.rb

Overview

rdoc

A Priority Queue is a data structure that behaves like a queue except that elements have an
associated priority. The #next and #pop methods return the item with the next highest priority.

Priority Queues are often used in graph problems, such as Dijkstra's Algorithm for shortest
path, and the A* search algorithm for shortest path.

This container is implemented using the Fibonacci heap included in the Collections library.

MIT License

Copyright (c) 2009 Kanwei Li

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

Instance Method Summary collapse

Constructor Details

#initialize(&block) ⇒ PriorityQueue

Create a new, empty PriorityQueue



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# File 'lib/containers/priority_queue.rb', line 38

def initialize(&block)
  # We default to a priority queue that returns the largest value
  block ||= lambda { |x, y| (x <=> y) == 1 }
  @heap = Containers::Heap.new(&block)
end

Instance Method Details

#clear ⇒ Object

Clears all the items in the queue.



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# File 'lib/containers/priority_queue.rb', line 65

def clear
  @heap.clear
end

#delete(priority) ⇒ Object

call-seq:

delete(priority) -> object
delete(priority) -> nil

Delete an object with specified priority from the queue. If there are duplicates, an arbitrary object with that priority is deleted and returned. Returns nil if there are no objects with the priority.

q = PriorityQueue.new
q.push("Alaska", 50)
q.push("Delaware", 30)
q.delete(50)            #=> "Alaska"
q.delete(10)            #=> nil



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# File 'lib/containers/priority_queue.rb', line 131

def delete(priority)
  @heap.delete(priority)
end

#empty? ⇒ Boolean

Returns true if the queue is empty, false otherwise.

Returns:

  • (Boolean) 


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# File 'lib/containers/priority_queue.rb', line 70

def empty?
  @heap.empty?
end

#has_priority?(priority) ⇒ Boolean

call-seq:

has_priority? priority -> boolean

Return true if the priority is in the queue, false otherwise.

q = PriorityQueue.new
q.push("Alaska", 1)

q.has_priority?(1)    #=> true
q.has_priority?(2)    #=> false

Returns:

  • (Boolean) 


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# File 'lib/containers/priority_queue.rb', line 84

def has_priority?(priority)
  @heap.has_key?(priority)
end

#next ⇒ Object

call-seq:

next -> object

Return the object with the next highest priority, but does not remove it

q = Containers::PriorityQueue.new
q.push("Alaska", 50)
q.push("Delaware", 30)
q.push("Georgia", 35)
q.next          #=> "Alaska"



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# File 'lib/containers/priority_queue.rb', line 98

def next
  @heap.next
end

#pop ⇒ Object Also known as: next!

call-seq:

pop -> object

Return the object with the next highest priority and removes it from the queue

q = Containers::PriorityQueue.new
q.push("Alaska", 50)
q.push("Delaware", 30)
q.push("Georgia", 35)
q.pop         #=> "Alaska"
q.size        #=> 2



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# File 'lib/containers/priority_queue.rb', line 113

def pop
  @heap.pop
end

#push(object, priority) ⇒ Object

Add an object to the queue with associated priority.

q = Containers::PriorityQueue.new
q.push("Alaska", 1)
q.pop #=> "Alaska"



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# File 'lib/containers/priority_queue.rb', line 60

def push(object, priority)
  @heap.push(priority, object)
end

#size ⇒ Object Also known as: length

Returns the number of elements in the queue.

q = Containers::PriorityQueue.new
q.size #=> 0
q.push("Alaska", 1)
q.size #=> 1



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# File 'lib/containers/priority_queue.rb', line 50

def size
  @heap.size
end