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 ato z.

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第一版答案

function printerError($s) {
    $arr = range('a', 'm');
    
    $s = str_split($s);
    
    $err = 0;
    for($i = 0; $i < count($s); $i++){
      if(!in_array($s[$i], $arr)){
        $err++;
      }
    }
    
    return $err . '/' . count($s);
}

function printerError($s) {
    return strlen(preg_replace('/[a-m]/i', '', $s)) . '/' . strlen($s);
}