937. Reorder Data in Log Files

Solution.java

class Solution {
  
  public String[] reorderLogFiles(String[] logs) {
    if (logs == null) {
      return null;
    }
    int n = logs.length;
    Map<String, String[]> map = new HashMap<>();
    for (String log : logs) {
      map.put(log, log.split(" ", 2)); // only consider the first word
    }
    // sorting
    Arrays.sort(logs, (s1, s2) -> {
      String[] log1 = map.get(s1);
      String[] log2 = map.get(s2);
      int type1 = Character.isDigit(log1[1].charAt(0)) ? 0 : 1; // 0 digit, 1 letter
      int type2 = Character.isDigit(log2[1].charAt(0)) ? 0 : 1;
      if (type1 == 0 && type2 == 1) {
        return 1;
      }
      else if (type1 == 1 && type2 == 0) {
        return -1;
      }
      else if (type1 == 0 && type2 == 0) { // both are digits
        return 0;
      }
      else { // both are letters
        int cmp = log1[1].compareTo(log2[1]);
        if (cmp == 0) return log1[0].compareTo(log2[0]); // identifier
        else          return cmp;
      }
    });
    
    return logs;
  }
  
}