input: Write a function to remove all consecutive duplicates from a given string. If the input string is empty return an empty string.
  assert remove_duplicates("")==""
  assert remove_duplicates("AAABBCCCD")=="ABCD"
  assert remove_duplicates("aabbbcccc")=="abc"
  assert remove_duplicates("xyz")=="xyz"
  assert remove_duplicates("a")=="a"
output: def remove_duplicates(s):
      if not s:
          return ""
      result = [s[0]]
      for char in s[1:]:
          if char != result[-1]:
              result.append(char)
      return ''.join(result)