The problem is, you could have as many as i (where i = 1 to n) "best candidates" at any time. Consider — if the list looks like this:

9 7 5 3 1 x
[download]

(i.e. you've processed all but the last number) you won't know until you look at the last number which of the preceding numbers (if any) are in the solution. x could be 10, or it could be 2, for example.

So you need to keep all the increasing subsequences seen so far; and that could be as many as n; and that means the algorithm is at least O(n log n).

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