Iterative vs. Recursive coding

[Martin Gregorie]

On Thu, 19 Aug 2010 14:12:44 -0700, Baba wrote:

> Level: Beginner
> 
> exercise source:
> http://ocw.mit.edu/courses/electrical-engineering-and-computer-
science/6-00-introduction-to-computer-science-and-programming-fall-2008/
assignments/pset3.pdf
> 
> I am looking at the first problem in the above assignment. The
> assignemnt deals, amongst others, with the ideas of iterative vs.
> recursive coding approaches and i was wondering what are the advantages
> of each and how to best chose between both options?
> 
> I had a go at the first part of the exercise and it seems that i can
> handle it. However i think my Recursive version can be improved. By the
> way, is my code actually proper recursive code?
>
No, it isn't. 

By way of a hint, here are two versions of the classic example of 
recursion: calculating factorials. Recursion can be quite a trick to get 
your mind round at first, so compare the two and follow through their 
operation step by step...

-------------------------------------------------

def i_factorial(n):
    "Iterative factorial calculation"
    f = 1;
    for n in range(1, n+1):
        f = f * n
    return f

def r_factorial(n):
    "Recursive factorial calculation"
    if (n > 1):
        return n * r_factorial(n - 1)
    else:
        return 1

print i_factorial.__doc__
for n in range(1,10):
    print "%d! = %d" % (n, i_factorial(n))

print r_factorial.__doc__
for n in range(1,10):
    print "%d! = %d" % (n, r_factorial(n))

-----------------------------------------

In case you're wondering "print i_factorial.__doc__" 
prints the docstring out of the i_factorial subroutine. 
You probably haven't covered that yet, but run it and see.


-- 
martin@   | Martin Gregorie
gregorie. | Essex, UK
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