Class: Containers::PriorityQueue

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

Overview

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.

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 15

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 42

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 108

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 47

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 61

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 75

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 90

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 37

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 27

def size
  @heap.size
end