code: private static List<Character[]> getLeetSub(final String password, final String unleet_password)
      {
          List<Character[]> leet_subs = new ArrayList<>();
          for (int i = 0; i < unleet_password.length(); i++)
          {
              if (password.charAt(i) != unleet_password.charAt(i))
              {
                  leet_subs.add(new Character[]{password.charAt(i), unleet_password.charAt(i)});
              }
          }
          return leet_subs;
      }
docs: Gets the substitutions for the password.
  
  @param password        the password to get leet substitutions for.
  @param unleet_password the password to get leet substitutions for.
  @return a {@code List} of {@code Character[]} that are the leet substitutions for the password.