8 Queens Problem

[Joseph A Knapka]

Simon.Foster at smiths-aerospace.com wrote:
> 
> Just For Fun!
> 
> I've been working on a solution to the eigth queens puzzle.
> Here is my attempt.  There's a solution in Scheme in SICP
> which takes only 13 lines.  Can anyone come up with a shorter
> solution in Python, without any of the obvious silliness?

Sure :-)

from operator import add
size=8
def attacks((r1,c1),(r2,c2)): return ((r1,c1) != (r2,c2)) and ((r1==r2)
or (abs(r1-r2)==abs(c1-c2)))
def check(n):
    qpos = map(lambda c: ((n/(size**c))%size,c),range(size))
    return reduce(add,[reduce(add,[attacks(qpos[q],qpos[o]) for o in
range(size)]) for q in range(size)])
for n in xrange(size**size):
    if not check(n): print "Solution:",map(lambda c:
((n/(size**c))%size,c),range(size))

It gives you the coordinates of the queens' board
positions, and finds all solutions by exhaustive search.
It isn't exactly fast, though. Set size=4 to solve
the 4-queens problem before you die. It exchanges
obvious silliness for obscure silliness. I'm sure Alex
can improve this lots.

Cheers,

-- Joe