Activity Selection

class Activity
  attr_accessor :s, :f
  def initialize(s,f)
    @s = s
    @f = f
  end
  def inspect
    "#{s} to #{f}"
  end
end

a = []
a << Activity.new(1,2)
a << Activity.new(3,4)
a << Activity.new(0,6)
a << Activity.new(5,7)
a << Activity.new(8,9)
a << Activity.new(5,9)

def select_activities(a)
  #sort by finish time
  a = a.sort_by(&:f)

  #select first activity
  result = []
  result << a.first

  #for each remaining activity
  i = 1
  until i == a.length
    if result.last.f <= a[i].s
      result << a[i]
    end
    i += 1
  end

  result
end
puts select_activities(a).to_s