937. Reorder Data in Log Files

class Solution {
    public String[] reorderLogFiles(String[] logs) {
        List<String> letterLogs = new ArrayList<>();
        List<String> digitLogs = new ArrayList<>();

        for (String log : logs){
            if (Character.isDigit(log.split(" ")[1].charAt(0))){
                digitLogs.add(log);
            } else {
                letterLogs.add(log);
            }
        }

        letterLogs.sort((s1,s2) -> {
            String[] s1x = s1.split(" ",2);
            String[] s2x = s2.split(" ",2);

            int compared = s1x[1].compareTo(s2x[1]);
            if (compared == 0){
                return s1x[0].compareTo(s2x[0]);
            } else {
                return compared;
            }
        });

        letterLogs.addAll(digitLogs);

        return letterLogs.toArray(new String[0]);
    }
}