PrinterError.rb

=begin

In a factory a printer prints labels for boxes. For one kind of boxes
the printer has to use colors which, for the sake of simplicity,
are named with letters from a to m.

The colors used by the printer are recorded in a control string.
For example a "good" control string would be aaabbbbhaijjjm meaning
that the printer used three times color a, four times color b,
then one time color a...

Sometimes there are problems: lack of colors, technical malfunction
and a "bad" control string is produced e.g. aaaxbbbbyyhwawiwjjjwwm.

You have to write a function printer_error which given a string will
output the error rate of the printer as a string representing a
rational whose numerator is the number of errors and the denominator
the length of the control string. Don't reduce this fraction to a
simpler expression.

The string has a length greater or equal to one and contains only
letters from ato z.

Examples:

s="aaabbbbhaijjjm"
error_printer(s) => "0/14"

s="aaaxbbbbyyhwawiwjjjwwm"
error_printer(s) => "8/22"

=end

# My Solution
def printer_error(s)
  good = s.count "abcdefghijklm"
  bad = s.count "nopqrstuvwxyz"
  (s.count "nopqrstuvwxyz").to_s ? "#{bad}/#{s.length}" : "0/#{good}"
end

# Better Solution
def printer_error(s)
  "#{s.count('n-z')}/#{s.length}"
end