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Priority queue implementation in Ruby
class PriorityQueue
attr_reader :elements
def initialize
@elements = [nil]
end
def <<(element)
@elements << element
bubble_up(@elements.size - 1)
end
def pop
exchange(1, @elements.size - 1)
max = @elements.pop
bubble_down(1)
max
end
private
def bubble_up(index)
parent_index = (index / 2)
return if index <= 1
return if @elements[parent_index] >= @elements[index]
exchange(index, parent_index)
bubble_up(parent_index)
end
def bubble_down(index)
child_index = (index * 2)
return if child_index > @elements.size - 1
not_the_last_element = child_index < @elements.size - 1
left_element = @elements[child_index]
right_element = @elements[child_index + 1]
child_index += 1 if not_the_last_element && right_element > left_element
return if @elements[index] >= @elements[child_index]
exchange(index, child_index)
bubble_down(child_index)
end
def exchange(source, target)
@elements[source], @elements[target] = @elements[target], @elements[source]
end
end
require 'minitest/autorun'
require_relative 'priority_queue'
class PriorityQueueTest < Minitest::Test
def setup
@priority_queue = PriorityQueue.new
end
def test_adds_element_in_correct_order
@priority_queue << 2
@priority_queue << 1
@priority_queue << 3
assert_equal [nil, 3, 1, 2], @priority_queue.elements
end
def test_removes_top_element
@priority_queue << 2
@priority_queue << 1
@priority_queue << 3
assert_equal 3, @priority_queue.pop
assert_equal [nil, 2, 1], @priority_queue.elements
end
end
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