#### Printer Errors

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, one time color h 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 `a`to `z`.

`#Examples:`
``s="aaabbbbhaijjjm"error_printer(s) => "0/14"s="aaaxbbbbyyhwawiwjjjwwm"error_printer(s) => "8/22"``

Returns an array of characters in str. This is a shorthand for `str.each_char.to_a`.
`def printer_error(s)     `
`  s_array = s.chars     colors = ['a', 'b', 'c', 'd', 'e' ,'f' ,'g' ,'h' ,'i' ,'j' ,'k' ,'l' ,'m']    `
`  total_count = s_array.count      bad_colors_count = s_array.reject{|x| colors.include?(x)}.count                   return new_s = "#{bad_colors_count}/#{total_count}"        end`

`def printer_error(s)     "#{s.count('n-z')}/#{s.size}" end`

#### s裡 n-z 出現的次數 / s的總字母數

Ruby 的字串有一個 `count` 方法，可簡單的算出字串中某些字母出現的次數

`words = "Lorem Ipsum Dolor Sit Amet, Consectetur Adipiscing Elit." `
`puts words.count("i")         # => 算出有幾個 i，共有 5 個 puts words.count("A-Z")       # => 算出所有大寫字母，共有 8 個 puts words.count("a-z")       # => 算出所有小寫字母，共有 39 個`