never give up!!

there are no elements to the left of index 0, so the left side of index 0 sums to 0.

in mathematics, the sum of an empty sequence is 0. this is natural if you want the formula sum(a + b + c + ...) = a + sum(b + c + ...) to be true in all cases; otherwise, this would not hold for sum(a).

Hmm, weird, it wasn't last time I checked, I've unflagged it now.

Read karenaf's post below.

The description says:

Your task is to return the first longest string consisting of k consecutive strings taken in the array.