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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