coach_stints.rb

require 'csv'
coach_years=CSV.read('coaches.csv')[1..-1]

def parse_coach_year(coach_year)
  start_year, end_year_suffix = coach_year[0].split('-')
  end_year_prefix = start_year < '2000' ? '19' : '20'
  end_year = "#{end_year_prefix}#{end_year_suffix}"
  return coach_year[1], start_year.to_i, end_year.to_i
end

i = 0
stints = coach_years.sort_by(&:reverse).each_with_object([]) do |coach_year, coach_stints|
  coach, start_year, end_year = parse_coach_year(coach_year)
  
  last_stint = coach_stints.last
  if [coach, start_year] == last_stint&.fetch_values(:coach, :end_year)
    last_stint[:end_year] = end_year
  else
    coach_stints << { coach: coach, start_year: start_year, end_year: end_year }
  end
end

stints.sort_by{|s| [s[:start_year], s[:end_year]]}