In problem 29 we are supposed to determine how many unique values there are for the value where , (all integers). I know there is clever counting one can do to determine this, but I thought for comparison I’d also just do up the brute force approach. Find all the values, get rid of duplicates, and count how many are left.

Python has a built-in type “set”, which will eliminate duplicates as I go. And you can ask for the length of the set. And list comprehension is awesome. So you can solve this in one line:

def solve(lowa, hia, lowb, hib):
return len(set([a**b for a in xrange(lowa, hia+1) for b in xrange(lowb, hib+1)]))

Having wrapped up solution code into a function, I also like to use command line arguments to pass in… well, arguments. In this case, I’d like to allow two different options for command line options. The stated problem has the bounds 2 to 100 for both and . So if I take one number in, I want to assume it is the upper bound, and that 2 is the lower bound, for both variables. Alternatively, I could take all four bounds in as arguments. I know the following is crude, and doesn’t fail gracefully, but it’s got a lot of nice things going for it:

if __name__ == "__main__":
if len(sys.argv) == 2:
print solve(*(2*[2,int(sys.argv[1])]))
else:
print solve(*map(int, sys.argv[1:]))

I love this. Using * to change a list into the form my solve function expects, with 4 arguments… that’s awesome. Using [1:] to grab the arguments besides the called command… nice. 2*list to do a list concatenated with itself… delightful. And, of course, map. Who could forget map?

Anyway, I may return to the more mathematical, counting based solution for this. At the same time, though, this code is quick (to write and run (for the stated bounds)) and easily checked. Maybe I’ll leave the more mathematical solution to the other authors on this blog. I seem to recall that there were some…

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Tags: nah, prob29, python

This entry was posted on September 29, 2009 at 9:18 pm and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed.
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