[Tutor] Automatic generation of an "all possible combinations" array

[Alan Gauld]

"Luke Paireepinart" <rabidpoobear at gmail.com> wrote

> You could also do this by iterating in base-16 instead of base-10...

I was going to suggest the same but using octal which
has the same property but fewer values to map. :-)

> hexmap = 
> {"0":"0000","1":"0001","2":"0010","3":"0011","4":"0100","5":"0101",
> "6":"0110","7":"0111","8":"1000","9":"1001","a":"1010","b":"1011","c":"1100",
> "d":"1101","e":"1110","f":"1111"}
>
> then for any number n,
> you simply do the following:
> binary = ""
> for x in hex(n)[2:]:
>  binary += (hexmap[x])
>
> this is very simple, but I am unsure how efficient it is.

Its very efficient, many of the C standard library routines (tolower 
etc)
use a similar technique. The amount of memory used is low and the
speed of a dictionary lookup is much less that multiple divisions etc
You can even avoid the dictionary and just use a list for octal since
n is the number of the index position, but I don't think list indexing 
is
any/much faster than a dictionary lookup in Python. (Time for timeit()
here I think...)

HTH,

-- 
Alan Gauld
Author of the Learn to Program web site
http://www.freenetpages.co.uk/hp/alan.gauld