Problem 45321. Kolakoski Sequence

So it's kind of like Kolakoski; the number still gives the length at pos n, like A000002. However, the following number is decided according to a base named "a". So, if a=[4,2,3], the remainder 0,1 or 2 (since a has length 3) will be mapped to 4,2,3 in this order.

I recommend solving the problem in the description if you haven't already. You can reuse your code here. You will need to make some changes, but it will be easier than solving this one from zero. Numberphile has a video about it if you are still stuck.

I fail to understand some of the examples, where the initial terms of the output are not the same as the input (a) -

a = [1,3,1,2];
x=30;
y=[1, 3, 3, 3,...] %first 4 terms of y not equal to a

a = [2,1];
x=10;
y=[2, 2, 1, ...] %first 2 terms of y not equal to a