class Containers::PriorityQueue

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.

Public Class Methods

new(&block) click to toggle source

Create a new, empty PriorityQueue

   # File lib/containers/priority_queue.rb
16 def initialize(&block)
17   # We default to a priority queue that returns the largest value
18   block ||= lambda { |x, y| (x <=> y) == 1 }
19   @heap = Containers::Heap.new(&block)
20 end

Public Instance Methods

clear() click to toggle source

Clears all the items in the queue.

   # File lib/containers/priority_queue.rb
43 def clear
44   @heap.clear
45 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
109 def delete(priority)
110   @heap.delete(priority)
111 end
empty?() click to toggle source

Returns true if the queue is empty, false otherwise.

   # File lib/containers/priority_queue.rb
48 def empty?
49   @heap.empty?
50 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
62 def has_priority?(priority)
63   @heap.has_key?(priority)
64 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
76 def next
77   @heap.next
78 end
next!()
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
91 def pop
92   @heap.pop
93 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
38 def push(object, priority)    
39   @heap.push(priority, object)
40 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
28 def size
29   @heap.size
30 end
Also aliased as: length