Maybe. But it is terribly easy in a high level language to use a built-in function that is O(N) and put in in a loop, and now you're at O(N^2). Maybe it works

Maybe. But it is terribly easy in a high level language to use a built-in function that is O(N) and put in in a loop, and now you're at O(N^2). Maybe it works in reasonable time for N=10,000. Maybe you test it on small data sets to see that it works. Now turn it loose on an N=10^7 dataset. Oh.