A permutation also called an “arrangement number” or “order,” is a rearrangement of the elements of an ordered list S into a one-to-one correspondence with S itself. A string of length n has n!

The permutations of a single-letter string is a set of one element, the single-letter string.

📌 Problem Statement: Given a string s (which may contain duplicate characters), generate and return all unique permutations of the string. The order of output doesn't matter, but duplicates must be ...