[tmerr]

Better to tune this out even if you're a beginner. You normally don't say "The big O of the algorithm is ..." because it's ambiguous whether you are talking about time complexity or space complexity. Also, when someone says O(n), then n has to refer to something, normally the input size. The text area doesn't even have you define your input, and will say things like

for (i =0; i<x; i++) { }

is O(N), without even knowing what x is (could be a constant).