Combinations and recursion, from an ASPN snippet
mwm at mired.org
Thu Mar 20 15:51:17 CET 2003
Andy Jewell <andy at wild-flower.co.uk> writes:
> I like to think of recursion as 'nesting' calls to the function, one inside
> the other:
> Hope this helps. The best way to learn recursion is to play with it. Use
> print statements liberally, and limit the recursion depth to a reasonable
> amount while you're at it - it's very hard to see what's going on when your
> program dumps 10 pages of output on the screen!
Combining these two things can be really useful. Keep a recursion
counter, and print spaces to indicate the depth of the recursion:
def recursive_add(m, n, depth = 0):
print " " * depth, m, n
if m < 0:
return -recursive_add(-m, n, 1)
elif m == 0:
return recursive_add(m - 1, n + 1, depth + 1)
Also, to get real headaches, look up ackerman's function. It's an
interesting demonstration of the power of recursion.
Mike Meyer <mwm at mired.org> http://www.mired.org/home/mwm/
Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.
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