[Tutor] To find the least number divisible by all numbers from 1-20
Hello All, Sorry for the earlier mail without subject. I was in a hurry so I missed that I am solving problem number 5 in project euler. I think my solution seems logically correct but it is not giving an answer as it is taking too long to execute. So can someone suggest an alternative solution? Here is my source code: import sys def check(num): lis=[20,19,18,17,16,14,13,11] #because a no. divisible by 20 is divisible by 2,4,5 and so on for the values omitted for i in lis: if num%i==0: continue else: return False break return True def main(): num=2520 # Because we can start from the no. divisible by 1-10 while not check(num): print(num) num+=2# Because num has to be even print(num) if __name__ == '__main__': main() ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] dbus.Array to string
On Tue, Aug 13, 2013 at 8:59 AM, Amit Saha wrote: > What does it mean (and will it always work?) when I don't specify any > encoding: > > >>> bytearray(ssid).decode() > u'BigPond679D85' > If you don't specify an encoding, then the default encoding is used; as you point out a bit later, your local default is ascii. Will it always work? NO. If there are any characters in the input stream (the SSID in this case), .decode will fail (probably with UnicodeDecodeError, but I can't test it at the moment.) I don't know the WiFi spec well enough to know whether you're ever going to run into non-ASCII characters in an SSID; I'm guessing that people in e.g. Russia name their networks in Cyrillic, but (despite living in a Russian neighborhood of Los Angeles) I've never seen any SSIDs that weren't pure ASCII. Does anybody out there know the rules for this? Just now I tried to change the SSID of my cell phone's mobile hotspot to Cyrillic, but the configuration utility wouldn't even let me change keyboards; I don't know, though, whether this is a limitation of the spec or just the local implementation. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] (no subject)
Hello All, I am solving problem number 5 in project euler. I think my solution seems logically correct but it is not giving an answer as it is taking too long to execute. So can someone suggest an alternative solution? Here is my source code: import sys def check(num): lis=[20,19,18,17,16,14,13,11] #because a no. divisible by 20 is divisible by 2,4,5 and so on for the values omitted for i in lis: if num%i==0: continue else: return False break return True def main(): num=2520 # Because we can start from the no. divisible by 1-10 while not check(num): print(num) num+=2# Because num has to be even print(num) if __name__ == '__main__': main() ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] To find the least number divisible by all numbers from 1-20
On Tue, Aug 13, 2013 at 9:45 AM, #PATHANGI JANARDHANAN JATINSHRAVAN# < jatinshr...@e.ntu.edu.sg> wrote: > Hello All, > > Sorry for the earlier mail without subject. I was in a hurry so I missed > that > > I am solving problem number 5 in project euler. I think my solution > seems logically correct but it is not giving an answer as it is taking too > long to execute. So can someone suggest an alternative solution? > My approach: factor each number from 1 to 20 (for example, 20 factors to 1, 2, 2, 5) and build a list of factors; for each number, check to see that the list contains enough copies of all of the current number's factors (e.g. four 2s and two 3s) and add them to the list if not; at the end, multiply the list of factors. It took me about a minute in Excel; about 45 minutes to work out my algorithm in Python - but it executed in less than a second. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] To find the least number divisible by all numbers from 1-20
On 13/08/13 17:45, #PATHANGI JANARDHANAN JATINSHRAVAN# wrote: def check(num): lis=[20,19,18,17,16,14,13,11] #because a no. divisible by 20 is for i in lis: if num%i==0: continue else: return False break return True This is a bit convoluted. All you need is for i in lis: if num%i != 0: return False return True def main(): num=2520 # Because we can start from the no. divisible by 1-10 while not check(num): print(num) num+=2# Because num has to be even Surely you can increment by 20 since that's the next number that is divisible by 20. eg if we start at 20 the next number divisible by 20 will be 40, not 22... That should speed up the search considerably! But my brain is nagging me that there should be a cleverer mathematical trick too, but I can't remember what it is... I'm sure one of our math gurus will tell us! :-) -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] To find the least number divisible by all numbers from 1-20
On 13/08/13 18:19, Alan Gauld wrote: On 13/08/13 17:45, #PATHANGI JANARDHANAN JATINSHRAVAN# wrote: def check(num): lis=[20,19,18,17,16,14,13,11] #because a no. divisible by 20 is for i in lis: if num%i==0: continue else: return False break return True This is a bit convoluted. All you need is for i in lis: if num%i != 0: return False return True Oops, that last return should be outside the loop, sorry... -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] [Spoiler alert] Re: To find the least number divisible by all numbers from 1-20
On Aug 13, 2013 7:21 PM, "Peter Otten" <__pete...@web.de> wrote: > > Peter Otten wrote: > > > I'll post a naive implementation of that idea in a follow-up. > > So there: > > def gcd(a, b): > if a == b: > return a > elif a > b: > return gcd(a-b, b) > else: > return gcd(a, b-a) > > N = 20 > numbers = range(2, N+1) > while len(numbers) > 1: > numbers.sort() > a, b = numbers[:2] > d = gcd(a, b) > numbers[:2] = [a*b//d] > result = numbers[0] > assert all(result % i == 0 for i in range(1, N+1)) > print result > > It turns out I can only avoid the recursion limit by sorting the numbers and > picking the smallest. For greater N you need to come up with a smarter > approach (the actual limit was N<=48) or at least a non-recursive > implementation of gcd(). I think it's better to compute the lcm by finding its prime factorisation. E.g. There are 4 twos in it since that's the maximum number of twos in the prime factorisation of any of the integers up to 20. I would post a snippet but isn't it generally a bit of a faux-pas to give solutions to these problems (I mean this as a real question)? Oscar > > ___ > Tutor maillist - Tutor@python.org > To unsubscribe or change subscription options: > http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] dbus.Array to string
On 14/08/13 02:49, Marc Tompkins wrote: On Tue, Aug 13, 2013 at 8:59 AM, Amit Saha wrote: What does it mean (and will it always work?) when I don't specify any encoding: bytearray(ssid).decode() u'BigPond679D85' If you don't specify an encoding, then the default encoding is used; as you point out a bit later, your local default is ascii. Will it always work? NO. If there are any characters in the input stream (the SSID in this case), .decode will fail (probably with UnicodeDecodeError, but I can't test it at the moment.) Careful -- you are confusing two distinct concepts here. ssid does not contain characters. It contains bytes. There are exactly 256 possible bytes, which are numbers 0, 1, ... 255. They may *represent* characters, or sounds, or images, or motion video, or any other form of data you like, in which case you have to ask (e.g.) "how is the sound encoded into bytes? is it a WAV file, or MP3, or OGG, or something else?" In this case, the ssid represents characters, but it contains bytes, and the same question applies -- how are the characters A, B, C, ... encoded into bytes? Unless you know which encoding is used, you have to guess. If you guess wrong, you'll get errors. If you're lucky you will get an exception, and know that you guessed wrong, but if you're unlucky you'll just get garbage characters. Fortunately, there are a couple of decent guesses you can make which will often be correct, at least in Western European countries, Australia, the USA, and similar: UTF-8 ASCII Latin-1 Latin-1 should be considered the "last resort" encoding, since it will never fail. But it can return garbage. UTF-8 should be considered your first guess, since it is the standard encoding that everyone should use. (Any application that doesn't use UTF-8 by default in the 21st century is, in my opinion, buggy.) I don't know the WiFi spec well enough to know whether you're ever going to run into non-ASCII characters in an SSID; A little bit of googling shows that it definitely happens, and that UTF-8 is the standard encoding to use. -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
