t = s = File.read("day05").chomp
v = ('a'..'z').map { |l| ["#{l}#{l.upcase}", "#{l.upcase}#{l}"] }.flatten
r = Regexp.union v
p r
while s.gsub!(r, '')
end
p s.size
# 9687 too high
p ('a'..'z').map { |l|
s = t.delete "#{l}#{l.upcase}"
while s.gsub!(r, '')
end
p [l, s.size]
s.size
}.min