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last updated:21thNov.2005

here you can get some sudoku files :

1) lists with my hardest sudokus:

you'll probably consider some of the sudokus in these lists as quite

easy, but the list as a whole should be hard for any program

or human. The challenge is: send me your list of hardest

sudokus and let's see whether my program solves your list

quicker than your program solves my list !

a) NEW !

87 hardest sudokus sorted by rating , they are hard for the new

as well as for the old program. Many new sudokus included from

Gordon Royle's list of 18-clues-sudokus ! topn87

b) 95 hardest sudokus sorted by rating: top95

(they are here mainly for historical reasons)

c) 234 hardest sudokus sorted by rating: topn234

d) 1465 hardest sudokus sorted by rating: top1465

e) 44 hardest 16*16 sudokus top44

topn.. - lists use the new rating program suexrat9.exe , see below

2) sudoku-programs :

my programs usually have their C-source-code attached to the executable.

If your editor can't handle this, you can uncover the attached

source code from my programs with this program: unattach

source-code of this program: unattach.c

a) sudoku-rating: suexrate

a1) sudoku-rating, new program; faster but less canonical suexrat9

b) sudoku-solving: suexk

c) sudoku-generating: suexg

d) sudoku-transforming: suexeq

(transforms a sudoku into an equivalent random sudoku with

same solving characteristics but different appearance)

e) find unavoidables in sudokugrids: unav27

f) find more unavoidables in sudokugrids: unav36

g) compute maximum cliques in intersection graphs: cliqo2l

h) program to solve "killer-sudokus": killer

i) program to search all sudokus with given mask for clues: suexmult

j) iterate through sudokus over a given grid to find minimum-clue-sudokus: suexsf

k) counts 3*3*9-sudokus: sud3d

l) enumerates the classes of the six 3*9-chutes in a sudokugrid: index416

(courtesy of Kjell Fredrik Pettersen)

m) exact-cover-solver for constraint-satisfaction-problems with alldifferent-constraints only: csp3

n) converts sudokus into SAT-instance in CNF: sud2sat

o) SATZ, SAT-solver from Li,Anbulagan to solve the converted sudokus: SATZ

p) Ed Russels' C-program to count the 6670903752021072936960 sudokugrids in 0.24sec. with 1GHz ! ed.c

q) program to solve latin-square-puzzles (QWH,QCP) qwh4

r) program to reduce sudokus to minimal suex9-

3) documentation

about solving exact-cover-problems using sudoku as an example: suexco.txt

"gang" of the 44 classes of 3*9 ordered sudoku-bands: 44-gang

23919 sudokus equivalent to their transpose, one from each class: t-invar.gz

306693 sudoku G-classes, one from each class: sudogan.gz

4) old lists with hard sudokus:

VB6-contest, topn88, top88, top89, top90, top91, top92, top93, top94, top95, top95eq, top96, top97, top100,

su16, top45, top46, top862, top870, top888, top2365, top1234, topn907, subig20(some easy ones too)

5) puzzles:

a) 100 random minmal 6-sudoku puzzles with explanation sudoku6

b) 50 random minimal 25*25 latin-square-puzzles qwhm25

c) locally minimal 25*25-sudoku min25

d) 12x12 queens-puzzle: sudo12.JPG

e) sudoku knight-tours: not yet

6.) copyright discussion:

no copyright on this webpage, on the programs or sudokus !

all my programs are public domain.

The sudokus are gathered from webpages, forums or generated by myself.

Some people claim copyright on sudokus,and some of these might be included

in some of my lists

I do think (and most others seem to agree) that sudokus are probably not

copyrightable in most countries, (for USA I estimate it at 90% probability)

collections of sudokus probably neither

but with somehow smaller likelyhood.(70%?)

The copyright laws are somehow unclear and you never know how a judge

will decide.

This could be somehow deliberate, so judges have more flexibility

in special cases, but it's absolutely unsatisfactory

since people don't know, what's allowed and what not !

see some discussions here:

copyright1

copyright2

copyright3

copyright4

copyright5

copyright6

and followups

copyright7

7.) links:

a) wikipedia,Sudoku

b) wikipedia,mathematics of sudoku

c) Gordon's minimum sudokus

c) forum d) vegard e) gordon f) frazer (to be completed later...)

send suggestions, bug-reports, corrections, ideas, feedback,...to:

sterten@aol.com