magicalclick said:

Sven Groot said:

*snip*

A lot of times you are required to use ONLY Big-O. That's why I am talking about this.

Required? By whom?

And Bass is right: assuming large n, the constants matter less. Let's assume n=1,000,000,000. That means with O(100n) it'd be 100,000,000,000. But with O(n^{2}), it's 1,000,000,000,000,000,000. With O(2^{n}) or O(n!), the numbers are so
large that Windows Calculator can't represent them anymore. Compare to that, a constant factor of 100 is peanuts.

And optimization (of the implementation, without changing the algorithm) can reduce the constants. But you can
*never* optimize it so that it improves the order without changing the algorithm. I can easily write two versions of quicksort where one is twice as fast as the other, but they'd both still be O(n log n). And I can
*never* do better than O(n log n) while still using quicksort. That's what Big-O is telling you. I can run it on a 286 16Mhz or on a Core i7 3Ghz, and even though it'd run much faster on the Core i7, it's still O(n log n).

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