3. Write a recursive function that prints all the permutations of a given string. For example, for the input "abcd" the function should print: abcd, abdc, acbd, acdb, adbc, adcb, bacd, bade, bcad, bcda, bdac, bdca, cabd, cadb, cbad, cbda, cdab, cdba, dabc, dacb, dbac, dbca, dcab, dcb