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Sum of distinct count of all subsets
Given an array $$$arr$$$ of length $$$N$$$, find the sum of count of unique values in a subset for every subset of $$$arr$$$, modulo $$$10^9 + 7$$$.
I can see that the result depends only on frequency of distinct values, and seems like some combinatorial trick, it's a made up question but seems standard, what is the most optimal solution for length $$$N$$$ array?
