The question gives all necessary data: what is an efficient algorithm to generate a sequence of K non-repeating integers within a given interval. The trivial algorithm (generating random numbers and, before adding them to the sequence, looking them up to see if they were already there) is very expensive if K is large and near enough to N.

The algorithm provided here seems more complicated than necessary, and requires some implementation. I've just found another algorithm that seems to do the job fine, as long as you know all the relevant parameters, in a single pass.