[EMAIL PROTECTED] writes:
> I'm trying to solve the 9-tile puzzle using as functional an approach
> as possible. I've recently finished reading SICP and am deliberately
> avoiding easy python-isms for the more convoluted scheme/functional
> methods. The following function is trivial to do with for loops and
> directly accessing arrays with [] syntax. I'm trying to limit myself
> to the types of idioms/semantics one finds in minimal scheme, such as
> in SICP. I want eventually to port this to scheme, but I know python
> better, so that's where I'm starting.
>
> My current problem is the following. The 9-tile puzzle consists of a
> list of lists like this [[1,2,3],[4,5,6],[7,8,0]], where the numbers
> can be jumbled up. I'm looking for the location of the zero using
> *only* recursion and operators that are similar to car/cdr. The
> return value should be the row,col of the zero. For example above
> the
> return value would be (2,2).
I'm not sure what your code does but there is a canonical way to
transform a loop the call of a recursive function. I don't think I can
put it into words easily so I've demonstrated it
below on your 'locate_zero' function.
def find_zero(square):
"The normal imperative way in simple Python."
i = 0
for row in square:
j = 0
for n in row:
if n == 0:
return i, j
j += 1
i += 1
def func_find_zero(square):
"""
The translation into recursive calls. A function is created for
each loop. There are no mutations.
"""
def square_loop(square, i):
def row_loop(row, j):
if row:
if row[0] == 0:
return i, j
else:
return row_loop(row[1:], j+1)
if square:
res = row_loop(square[0], 0)
if res is not None:
return res
else:
return square_loop(square[1:], i+1)
return square_loop(square, 0)
I've intentionally made both function 'non-clever' to make the translation
process more apparent.
--
Arnaud
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