E x a c t l y .

Thanks for writing, I had this problem.

Exactly.

The longest non-negative sequence is 5 in the example you provided. you think it's 7 because you mistakenly omitted one of the -1 values in the sequence.

-1, -1, 0, 0, 0, 1, -1, -1, -1, 1   #input
                         ^
                        where did this -1 go in your answer?
        0, 0, 0, 1, -1,     -1, 1 

return the size of the longest sub-section with a sum of zero or higher.

You can suggest some clarification in the description if it's not clear enough. Sequence vs sub-section for instance.

As Chrono79 explained, 5 is the correct answer for that input.

It seems it's Python:

-1, -1, 0, 0, 0, 1, -1, -1, -1, 1
                         ^                       

There are three -1 in a row there, the expected answer of 5 is ok 0, 0, 0, 1, -1

 0, 0, 0, 1, -1      -1, 1

Those are 2 sub-sections.

which language?