public static int alternatingCharacters(String s) {
  if (s.length() <= 1) {
    return 0;
  }

  int deletions = 0;

  for (int i = 1; i < s.length(); i++) {
    if (s.charAt(i) == s.charAt(i - 1)) {
      deletions++;
    }
  }
  return deletions;
}