# Shellsort algorithm,
# see examples in test/shell_sort_test.rb
module Shell
  def self.sort(array)
    gap = 1
    gap = 3 * gap + 1 while gap < array.size / 3

    while gap > 0
      gap.upto(array.size - 1) do |i|
        j = i
        while j > 0 && array[j] < array[j - gap]
          array[j], array[j - gap] = array[j - gap], array[j]
          j -= gap
        end
      end

      gap /= 3
    end

    array
  end
end