The museum has a guest book at the door, and people sign it every time they come in, so one person may sign several times a day. Write unique_visitors(stamps) to return how many different people came today. An empty book gives 0.
unique_visitors(["Mia", "Leo", "Mia"])→2unique_visitors([])→0def unique_visitors(stamps):
# your code here: put the names in a set and count it
return 0
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