print(count_unique([ ]))
print(count_unique(['h']))
print(count_unique(['a','a','b','b','c','c'  ]))
print(count_unique([ 'a','b','c' ]))
print(count_unique([null ]))
print(count_unique([ 'a','b','c','c','c','d','e','f','g','g','g','h']))

