Discussion on: Daily Challenge #296 - Years to Centuries

View post

This might be a bit over-engineered, but here is another Ruby solution:

def to_century(year)
  (year.to_i / 100 + 1).english.ordinal
end

class Integer
  def english
    English::Integer.new(self)
  end
end

module English
  class Integer    
    def initialize(integer)
      @value = integer
    end

    ##
    # Returns ordinal notation of the current integer ("-2nd", "1st", "312th").
    def ordinal
      "#{@value}#{ordinal_suffix}"
    end

    ##
    # Returns the ordinal suffix of the current integer ("st", "nd", "rd", "th").
    def ordinal_suffix
      case @value.abs % 100
      when 1, 21, 31, 41, 51, 61, 71, 81, 91 then 'st'
      when 2, 22, 32, 42, 52, 62, 72, 82, 92 then 'nd'
      when 3, 23, 33, 43, 53, 63, 73, 83, 93 then 'rd'
                                             else 'th'
      end
    end
  end
end

Which produces the following output:

years = %w[8120 30200 1601 2020 3030 1900 1776]
years.to_h { |year| [year, to_century(year)] }
#=> {"8120"=>"82nd", "30200"=>"303rd", "1601"=>"17th", "2020"=>"21st", "3030"=>"31st", "1900"=>"20th", "1776"=>"18th"}