class Containers::PriorityQueue

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
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SOFTWARE.

Public Class Methods

new(&block) click to toggle source

Create a new, empty PriorityQueue

# 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

Public Instance Methods

clear() click to toggle source

Clears all the items in the queue.

# File lib/containers/priority_queue.rb, line 65
def clear
  @heap.clear
end
delete(priority) → object click to toggle source
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
# File lib/containers/priority_queue.rb, line 131
def delete(priority)
  @heap.delete(priority)
end
empty?() click to toggle source

Returns true if the queue is empty, false otherwise.

# File lib/containers/priority_queue.rb, line 70
def empty?
  @heap.empty?
end
has_priority? priority → boolean click to toggle source

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
# File lib/containers/priority_queue.rb, line 84
def has_priority?(priority)
  @heap.has_key?(priority)
end
length()
Alias for: size
next → object click to toggle source

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"
# File lib/containers/priority_queue.rb, line 98
def next
  @heap.next
end
Alias for: pop
pop → object click to toggle source

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
# File lib/containers/priority_queue.rb, line 113
def pop
  @heap.pop
end
Also aliased as: next!
push(object, priority) click to toggle source

Add an object to the queue with associated priority.

q = Containers::PriorityQueue.new
q.push("Alaska", 1)
q.pop #=> "Alaska"
# File lib/containers/priority_queue.rb, line 60
def push(object, priority)
  @heap.push(priority, object)
end
size() click to toggle source

Returns the number of elements in the queue.

q = Containers::PriorityQueue.new
q.size #=> 0
q.push("Alaska", 1)
q.size #=> 1
# File lib/containers/priority_queue.rb, line 50
def size
  @heap.size
end
Also aliased as: length