Great solution!
But why u dont want use the "readable" variable names in reduce?)

bravissimo

And where is the case when a=b=c=n?

I don't like the fact that you call the lengths many times instead of having them in a variable

Clever but not needed

damnnn, best solution so far

it's a bad practice to use a ternary operator in this case, isn't it?

it is unusual solution

Great formatting! This is how I solved it as well

I like this rather than just endWith