title: How to count unique integers in unordered_set?
body: <p>A question that might appear trivial, but I am wondering if there's a way of obtaining the count of integers made unique after I transform an array containing repeated integers into an unordered_set. To be clear, I start with some array, turn into an unordered set, and suddenly, the unordered_set only contains unique integers, and I am simply after the repeat number of the integers in the unordered_set.
  Is this possible at all? (something like unordered_set.count(index) ?)</p>