sort logs

Pair.java

    class Pair<T,S> {
        T fst;
        S snd;
        public Pair(T fst, S snd) {
            this.fst = fst;
            this.snd = snd;
        }
    }

PairComparator.java

    class PairComparator implements Comparator<Pair<String, String>> {
        @Override
        public int compare(Pair<String, String> x, Pair<String, String>  y) {
            if (x.snd.equals(y.snd)) {
                return x.fst.compareTo(y.fst);
            }
            else {
                return x.snd.compareTo(y.snd);
            }
        }

    } 

sortLogs.java

sortLogs(String[] logs) {
        if (logs == null) {
            return logs;
        }

        if (logs.length < 2) {
            return logs;
        }

        List<String> digitLog = new ArrayList<>();
        List<Pair<String, String>> letterLog = new ArrayList<>();
        for(String log : logs) {
            String[] words = log.split(" ");
            String separatedData = String.join(" ", Arrays.copyOfRange(words, 1, words.length) );
            if (separatedData.matches(".*\\d.*")) {
                digitLog.add(log);
            }
            else {
                Pair<String, String> pair = new Pair<>(words[0], separatedData);
                letterLog.add(pair);
            }
        }
        Collections.sort(letterLog, (a,b)->  (a.snd).equals(b.snd) ? a.fst.compareTo(b.fst) : a.snd.compareTo(b.snd));

        int i = 0;
        String[] response = new String[logs.length];
        for(Pair<String, String> logLetter : letterLog) {
            StringBuilder sb = new StringBuilder();
            sb.append(logLetter.fst).append(" ").append(logLetter.snd);
            response[i++] = sb.toString();
        }

        for(String digitLetter : digitLog) {
            response[i++] = digitLetter;
        }
        return response;
    }

sortLogsPQ.java

sortLogs2(String[] logs) {
        if (logs == null) {
            return logs;
        }

        if (logs.length < 2) {
            return logs;
        }

        Comparator<Pair<String, String>> comparator = new PairComparator();
        PriorityQueue<Pair<String, String>> priorityQueue = new PriorityQueue<>(logs.length, comparator);
        List<String> digitLog = new ArrayList<>();
        for(String log : logs) {
            int firstBlackSpace = log.indexOf(' ');
            String logKey =  log.substring(0, firstBlackSpace);
            String separatedData = log.substring(firstBlackSpace + 1);                  
            if (separatedData.matches(".*\\d.*")) {
                digitLog.add(log);
            }
            else {
                Pair<String, String> pair = new Pair<>(logKey, separatedData);
                priorityQueue.add(pair);
            }
        }
        //Collections.sort(letterLog, (a,b)->  (a.snd).equals(b.snd) ? a.fst.compareTo(b.fst) : a.snd.compareTo(b.snd));

        String[] response = new String[logs.length];
        int i = 0;
        while (priorityQueue.size() != 0) {
            Pair<String, String> logLetter = priorityQueue.remove();
            StringBuilder sb = new StringBuilder();
            sb.append(logLetter.fst).append(" ").append(logLetter.snd);
            response[i++] = sb.toString();
        }


        for(String digitLetter : digitLog) {
            response[i++] = digitLetter;
        }
        return response;
    }