Trivial map/filter/reduce is not a novel kata idea.

hmm, I guess I've done match the same, but more complicated :) Nice solution https://www.codewars.com/kata/reviews/5a5e23c47635599816000ac8/groups/5d166b37fdfc750001de6dd3

Input range of n is not specified. What if n is zero, or negative? There should at least be a test for this.

Needs random tests

The same

Have you already realised what's wrong in your question? Those params are refer to lambda "sum" function. Not to accumulate.

The system of equations to solve is

x - 2y = i
x + 2y = j

which leads to

x = (j+i)/2
y = (j-i)/4

Looks a bit complicated... )

Looks nice

This is not tail recursive, and as such is not optimized well. If the list is long, you'd end up with a stack overflow.

What about built-in int64 type for tests?

What about capital letters?

OK, good point ;-)
Added this to description:

draw([1,0,1,0,1,0,1,0])

■□■□■□■□

And added this to testcase:

var wave5=
"■□■□■□■□";

Test.assertSimilar(draw([1,0,1,0,1,0,1,0]), wave5)

Thanks for your feedback ;-)