merge_sort.rb

# frozen_string_literal: true

# Sort an array using the MergeSort algorithm
class MergeSort
  attr_reader :array_sorted

  def initialize
    @array_sorted = []
  end

  def init(array)
    sort(array)
  end

  private

  def sort(array)
    return array if array.length <= 1

    mid = (array.length / 2).round

    left  = array.take(mid)
    right = array.drop(mid)

    sorted_left = sort(left)
    sorted_right = sort(right)

    @array_sorted = merge(sorted_left, sorted_right)
  end

  def merge(left, right)
    return left if right.empty?
    return right if left.empty?

    small_number = if left.first <= right.first
                     left.shift
                   else
                     right.shift
                   end

    recursive = merge(left, right)

    [small_number].concat(recursive)
  end
end

# test
m = MergeSort.new
m.init([1, 4, 10, 2, 3, 32, 0])
p m.array_sorted