On 09/15/2012 11:48 PM, aklei...@sonic.net wrote:
>> On 09/15/2012 10:03 PM, Scurvy Scott wrote:
>>>> That list would fill all the PC's on the planet a few billions times.
>>>> The number of items in the list has 25 digits in it. print 32**16
>>>>
>> I can't see any reason why it changes anything. The world doesn't have
>> enough disk space to store *every* address. If you need to calculate
>> all of them, you don't have enough time.
>>
>> You need to rethink whatever your real problem is. For example, if you
>> were really trying to crack a safe with 32 numbers on the dial and 16
>> settings to open it, perhaps you should forget all of it and get some
>> nitro. Or a stethoscope. Or bribe somebody who knows the combination.
>> If you have to try all of the combinations systematically, you'll never
>> get there.
> We can probably all agree that there aren't enough resources (time,
> memory, etc) to solve the problem, but that doesn't make the problem
> uninteresting.
> What interests me, and I acknowledge that this is more a question for a
> computer science forum than a python one, is: can this be done in a non
> recursive way so the limiting factor will be time, not memory? I couldn't
> think of a way.
>
it can certainly be done non-recursively, as I showed with a relatively
simple list comprehension, borrowing the idea from Peter Otten.
import itertools
chars = "ab5"
result = ["".join(item) for item in itertools.product(*[chars]*4)]
Non-recursive doesn't mean "uses little memory," however.
Since the problem is to build a list, it will use lots of memory. If
the problem were instead to make a generator that yields all possible
strings,
import itertools
chars = "ab5"
result_generator = ("".join(item) for item in itertools. product(*[chars]*4))
Now, you could write a loop that examined all these items (pretending
you had unlimited time), something like:
for item in result_generator:
if test_safe(item):
print item, "cracked the algorithm"
obviously, you'd need a longer chars, and to change *4 to *16, if you
actually wanted to do the original dataset.
And if you don't want to use itertools, you can trivially do it in a
loop, since you're basically just counting, base 32.
--
DaveA
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