Arithmetic Progression

ap.rb

@n = 3
@sequence = '0 8 12'.split(' ').map(&:to_i).sort

def ratio
  (@sequence[-1] - @sequence[0])/@n.to_i
end

def missing(n, sequence, diff)
  numbers = []
  n.times do |c|
    numbers << sequence[0] + ((c+1) - 1)*diff
  end
  puts numbers - sequence
end

missing(@n, @sequence, ratio)