I would argue that it’s O(n), increasing linearly with number of pages of the document ;-).
I see where you're coming from and we're probably getting wayyy in the weeds on this...:)....but I think they mean an insert of item into already existing array is O(1) and from your perspective ..traversal over time would be O(n) so I think y'all might both correct from diff perspectives.
I was thinking increasing insert time would increase Big O but they made the point that it's a constant which will cancel out as n approaches infinity.
God I'm a nerd.
HA. True I guess it just adds a constant to capture time . Good catch.