input: Write a python function to check if a string contains at least two distinct characters.
  assert containsTwoDistinctChars("AbcdABC") == True
  assert containsTwoDistinctChars("A") == False
  assert containsTwoDistinctChars("Aa") == True
  assert containsTwoDistinctChars("") == False
output: def containsTwoDistinctChars(s):
      return len(set(s)) >= 2