Dutch Sint Maarten: the official currency is the Netherlands Antillean Floren, but all merchants with whom you will be dealing will have prices marked in U.S. dollars and will accept your U.S. dollars and give you change in U.S. currency.
French Saint Martin: the official currency is the French Franc, but all merchants with whom you will be dealing will have prices marked in U.S. dollars and will accept your U.S. dollars and give you change in U.S. currency.
Ironically, although U.S. dollars are accepted on both sides of St Maarten, the French currency is not accepted on the Dutch side, and the Dutch currency is not accepted on the French side.