OK, I have a nice, easy question that will let you show off your cleverness (I could do this easily by brute force, but I want some efficiency, as I will have to do it thousands of times).

I have some random strings (actually hex strings, but I would like to see a more general case). I want to find the number of unique characters in the string.

f(0101010101) should return 2
f(1234567812) should return 8

In reply to number of unique characters in a string by Anonymous Monk

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