cubs.rb

class Odds
  def initialize
    @teams = {ari: 1998, atl: 1871, bal: 1901, bos: 1901, chc: 1874, cws: 1901,
              cin: 1882, cle: 1901, col: 1993, det: 1901, fla: 1993, hou: 1962,
              kan: 1969, laa: 1961, lad: 1884, mil: 1969, min: 1901, nym: 1962,
              nyy: 1901, oak: 1901, phi: 1883, pit: 1882, sd: 1969, sea: 1977,
              sf: 1883, stl: 1882, tb: 1998, tex: 1961, tor: 1977, was: 1969}
  end

  def tally_teams_given_year(year)
    @teams.values.select { |y| y <= year }.count
  end

  def probability_of_losing_between_years(begin_year, end_year)
    (begin_year..end_year).reduce(1.0) do |accum, el|
      tally = tally_teams_given_year(el)
      tally > 1 ? accum * ((tally - 1.0) / tally) : accum
    end
  end
end