lines = File.read("day2").split("\n")
lines.pop

def count_changes(s1, s2)
  pairs = s1.chars.zip s2.chars
  total = 0
  pairs.each do |pair|
    total += 1 if pair[0] != pair[1]
  end
  return total
end

lines.product(lines).each do |pair|
  puts "#{pair[0]}, #{pair[1]}" if count_changes(pair[0], pair[1]) == 1
end