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
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
Clears all the items in the queue.
# File lib/containers/priority_queue.rb 43 def clear 44 @heap.clear 45 end
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
Returns true if the queue is empty, false otherwise.
# File lib/containers/priority_queue.rb 48 def empty? 49 @heap.empty? 50 end
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
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
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
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
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