> a single accumulator register per counted entity.
That requires O(n) memory space, where n is the number of counted entities. If you're willing to spend this much memory, the problem is easy. Algorithms like the one in the article (or the paper I mentioned) are for when you want to use far less memory than that.
Count-min sketches can be adapted to use exponential decay. Presumably any sort of recurrent decay could be used to get approximately rectangular windows as well.
That requires O(n) memory space, where n is the number of counted entities. If you're willing to spend this much memory, the problem is easy. Algorithms like the one in the article (or the paper I mentioned) are for when you want to use far less memory than that.