What sort does Java Collections.sort(nodes) use?

Question

I think it is MergeSort, which is O(n log n).

However, the following output disagrees:

-1,0000000099000391,0000000099000427
1,0000000099000427,000000         


        

Answer 1

An algorithm A(n) that processes an amount of data n is in O(f(n)), for some function f, if there exist two strictly positive constants C_inf and C_sup such that:

C_inf . f(n) < ExpectedValue(OperationCount(A(n))) < C_sup . f(n)

Two things to note:

• The actual constants C could be anything, and do depend on the relative costs of operations (depending on the language, the VM, the architecture, or your actual definition of an operation). On some platforms, for instance, + and * have the same cost, on some other the later is an order of magnitude slower.

• The quantity ascribed as "in O(f(n))" is an expected operation count, based on some probably arbitrary model of the data you are dealing with. For instance, if your data is almost completely sorted, a merge-sort algorithm is going to be mostly O(n), not O(n . Log(n)).