Shawn Milochik wrote:

> On Jan 23, 2008, at 10:02 PM, Derek Marshall wrote:

>

>> This is just for fun, in case someone would be interested and because

>> I haven't had the pleasure of posting anything here in many years ...

>>

>> http://derek.marshall.googlepages.co...onsudokusolver

>>

>> Appreciate any feedback anyone who takes the time to have a look would

>> want to give ...

>>

>> Yours with-too-much-time-to-kill-on-the-train'ly,

>> Derek

>> --

>> http://mail.python.org/mailman/listinfo/python-list

>

> For those interested in this topic, here's another (much shorter) one:

>

> http://norvig.com/sudoku.html

>

> I'm not making any judgements here, though. If anyone takes the time

> to actually review them, I'd be interested in hearing any educated

> comparisons.

>

> Shawn
So would I. Below is the "winner" of my hacking for an as fast as possible 110%

pure python (no imports at all!) comprehensive sudoku solver under 50 LOCs, back

in 2006. Performance is comparable to the solver you advertize - numbers are

slightly better, but platform differences could easily absorb that - eg (not

counting module initialization and not using psyco) it takes 9.3 ms average on

the "AI escargot" problem linked to in Norwig's page, 5.6 ms/problem on some

standard "top1465" list of hard problems, and 3.4 ms/problem on the first 1000

on some other "top50000" list of relatively hard problems. This on my 2GHz Intel

Centrino '05 laptop. Psyco reduces times by about 50%. Dropping performance

requirements by half allows reducing LOC count in proportion.

OTOH, the code although short is nearly unreadable, sorry; should probably

feature/comment it on some web page, like the two already proposed in the

thread. Will do if/for reviewer. Interface is calling sudoku99(problem) with

'problem' a standard 81 character string with '0' or '.' placeholder for

unknowns. Returns same with values filled in.

Beware that although in practice it solved all well-formed human-solvable

problems I could find, it is not guaranteed to deal properly (or even

terminate?) for underdetermined problems or determined problems that would

require exploring choicepoints with more than 2 possibilities (if such exist).

Cheers, Boris

w2q = [[n/9,n/81*9+n%9+243,n%81+162,n%9*9+n/243*3+n/27%3+81]

for n in range(729)]

q2w = (z[1] for z in sorted((x,y) for y,s in enumerate(w2q) for x in s))

q2w = map(set,zip(*9*[q2w]))

w2q2w = [set(w for q in qL for w in q2w[q] if w!=w0) for w0,qL in enumerate(w2q)]

empty = set(range(729)).copy

def sudoku99(problem) :

givens = set(9*j+int(k)-1 for j,k in enumerate(problem) if '0'<k)

ws=search(givens,[9]*len(q2w),empty())

return ''.join(str(w%9+1) for w in sorted(ws))

def search(w0s,q2nw,free) :

while 1 :

while w0s:

w0 = w0s.pop()

for q in w2q[w0] : q2nw[q]=100

wz = w2q2w[w0]&free

free-=wz

for w in wz :

for q in w2q[w] :

n = q2nw[q] = q2nw[q]-1

if n<2 :

ww,=q2w[q]&free

w0s.add(ww)

if len(free)==81 : return free

thres = int((len(free)+52.85)/27.5)

ix,vmax = -1,0

try :

while 1 :

ix=q2nw.index(2,ix+1)

for w0 in (q2w[ix]&free)-w0s :

v = len(w2q2w[w0]&free)

if v > vmax :

ixmax = ix

if v >=thres : break

vmax = v

w0s.add(w0)

else : continue

break

except : pass

w0,w1 = q2w[ixmax]&free

try :

w0s.clear()

w0s.add(w0)

return search(w0s,q2nw[:],free.copy())

except ValueError :

w0s.clear()

w0s.add(w1)