>>>>> "rgalgon" == rgalgon <[EMAIL PROTECTED]> writes:
rgalgon> I'm new to Python and have been putting my mind to learning it rgalgon> over my holiday break. I've been looking over the functional rgalgon> programming aspects of Python and I'm stuck trying to come up with rgalgon> some concise code to find Taxicab numbers rgalgon> (http://mathworld.wolfram.com/ TaxicabNumber.html). rgalgon> "Taxicab(n), is defined as the smallest number that can be rgalgon> expressed as a sum of two positive cubes in n distinct ways" rgalgon> In Haskell something like this could easily be done with: rgalgon> cube x = x * x * x rgalgon> taxicab n = [(cube a + cube b, (a, b), (c, d)) rgalgon> | a <- [1..n], rgalgon> b <- [(a+1)..n], rgalgon> c <- [(a+1)..n], rgalgon> d <- [(c+1)..n], rgalgon> (cube a + cube b) == (cube c + cube d)] rgalgon> I'm looking for a succinct way of doing this in Python. I've been rgalgon> toying around with filter(),map(), and reduce() but haven't gotten rgalgon> anything half-way decent yet. rgalgon> So, how would you implement this taxicab(n) function in Python? To give a fairly literal translation of your Haskell, you could just use this: def cube(n): return n ** 3 def taxicab(n): n += 1 return [(cube(a) + cube(b), (a, b), (c, d)) for a in xrange(1, n) for b in xrange(a + 1, n) for c in xrange(a + 1, n) for d in xrange(c + 1, n) if cube(a) + cube(b) == cube(c) + cube(d)] If you print the return value of this you get the same results as your Haskell examples. I added the following to my Python file: if __name__ == '__main__': import sys print taxicab(int(sys.argv[1])) Then I see $ time taxicab.py 20 [(1729, (1, 12), (9, 10)), (4104, (2, 16), (9, 15))] real 0m0.098s user 0m0.046s sys 0m0.046s Terry -- http://mail.python.org/mailman/listinfo/python-list
