## Daily Challenge

Multisets are allowed to have repeated elements. A multiset of $$n$$ items may thus have fewer than $$n!$$ distinct permutations. For example, $$\{1,1,2,2\}$$ has only six permutations: $$(1,1,2,2), (1,2,1,2), (1,2,2,1), (2,1,1,2), (2,1,2,1), (2,2,1,1)$$ Design and implement an efficient algorithm for constructing all permutations of a multiset.

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