It perfectly feasible to pre-allocate the bitstrings to their largest possible size

That's cheating, in some sense.

If you consider all limitation of real machines, you will find that perl can only ever handle a fixed, finite amount of RAM (if the pointers are 64 bit, it's 2**64), every list is limited by that, so every of the mentioned algorithms runs in O(1). Just with a very big constant.

That's why you usually rely on the model of an ideal machines (works with bigints, and arbitrarily much RAM) for the run time analysis.

In reply to Re^4: Fast, Efficient Union and Intersection on arrays by moritz
in thread Fast, Efficient Union and Intersection on arrays by barvin

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