Problem
Given a range of integers $\{a,a+1,...,b-1,b\}$, find a subset of size $k$ such that the sum is equal to $s$.
Question
This problem came from evaluating some scheduling algorithms that I am interested in optimizing for some small home grown useless embedded system I am playing with. My problem is that I do not know if this problem is NP-Complete like the K-Sum problem. I am guessing it might be but it has been a while since I have dealt with proofs pertaining to NP problems. I remember something with SAT, but looking around did not jog any memories (at least any good ones).
How might I prove it is or is not NP-Complete?