code: private void addMinMax(String chars) {
          for (int i = 0; i < chars.length(); i++) {
              int c = chars.codePointAt(i);
              if (min == -1 || min > c) {
                  min = c;
              }
              if (max == -1 || max < c) {
                  max = c;
              }
          }
      }
docs: Updates {@code min} and {@code max} so that the range {@code min..max}
  includes all values from {@code chars}.
  
  @param chars
  the list of characters to process.