Worst-case

(∑_(dif=0)^(n-2))(∑_(i=1)^(n-dif))2(dif+1)

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Best case

(∑_(dif=0)^(n-2))(∑_(i=1)^(n-dif))(dif+2)

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So, in any case, Θ((n^3))