On Fri, 1 May 2015 05:23 pm, Jon Ribbens wrote: > On 2015-04-30, Dave Angel <da...@davea.name> wrote: >> On 04/30/2015 07:31 PM, Jon Ribbens wrote: >>> On 2015-04-30, Dave Angel <da...@davea.name> wrote: >>>> But the real reason I didn't like it was it produced a much larger >>>> set of happy_numbers, which could clog memory a lot sooner. For >>>> 10**7 items, I had 3250 happy members, and 19630 unhappy. And Jon >>>> had 1418854 happy members. >>> >>> Er, what? You're complaining that mine is less efficient by not >>> producing the wrong output? >> >> It's not intended as a criticism; you solved a different problem. The >> problem Cecil was solving was to determine if a particular number is >> happy. The problem you solved was to make a list of all values under a >> particular limit that are happy. >> >> Both produce identical results for the Cecil purpose, and yours is >> faster if one wants all the values. But if one wants a sampling of >> values, his function will fetch them quickly, and even if you want them >> all, his function will use much less memory. > > I must admit, I'm still not understanding. If you want to know only > whether or not int(1e7) is happy then the calculation takes no > measurable time or memory.
Oh, I'm sure somebody would be able to measure it... Rather than 10**7, how about trying (10**500 + 2). Is it happy? Using the Python code from Wikipedia: https://en.wikipedia.org/wiki/Happy_number SQUARE = dict([(c, int(c)**2) for c in "0123456789"]) def is_happy(n): while (n > 1) and (n != 4): n = sum(SQUARE[d] for d in str(n)) return n == 1 I can calculate whether n=10**500 + 2 is happy in less than a millisecond on my computer. Using your version doesn't even work, as it would require significantly more than 1000 terrabytes of RAM just to hold the results. I don't have that much memory. Your version is a reasonable answer to a different question, but it doesn't scale to very large inputs. -- Steven -- https://mail.python.org/mailman/listinfo/python-list
