The World's Hardest Sudoku (June 2012)

[Zapmeister]

Re: The World's Hardest Sudoku (June 2012)

Guess and check = guess a number and try to solve.
Logic = guess a number and try to solve in your head.

The only difference is that with logic you don't get a paper full of eraser residue.

Or you could just redraw the grid out.

There aren't any precise definitions anywhere of what constitutes solving logically and what is guess-and-check. Your definition is as good as any. (Though having a "definition" that depends on your mental capacity isn't exactly ideal)

However, part of the ambiguity lies in the fact that there's no consensus on whether the whole point of sudoku is to prove that there is a unique solution, or whether given a unique-solution puzzle to find it. In the former case, when you guess a number and it gets to a solution you have to discard it.

Put a number in a square, if it doesn't work, it's the wrong number kpCE

You're assuming that you can get anywhere. With some of the hardest puzzles, like the one presented in the OP, there comes a point at which wherever you guess you will not be able to progress anywhere so you won't be able to prove or disprove any possible candidates.

WHAT DO YOU DO NOW, HUH? :P

also try this one for size, just discovered last week, and there is a clever one-step logical solution but if you really want to brute force it go ahead

...|.5.|7..
...|9.1|.6.
...|...|..5
---+---+---
2..|..8|.16
...|...|.2.
.3.|...|4.7
---+---+---
.7.|.4.|...
..8|2.9|...
9.6|8..|...

SE 11.7

in other news katy perry is bad at sudoku

http://www.youtube.com/watch?v=KlyXNRrsk4A#t=86s

[gold stinger]

Re: The World's Hardest Sudoku (June 2012)



lol

[Choofers]

Re: The World's Hardest Sudoku (June 2012)

ironically, we have Sudoku puzzles as supplementary exercises to do after we're done with the course material

it's supposed to teach us logic and how to implement that logic into algorithms, whether it's mathematical algorithms we figure out on paper or something we write in a scripting language (bash, powershell, etc), as well as how to look for certain patterns (oddly this has helped me see patterns in complex subnetting, routing tables, and registry settings when it comes to ad schema)

So I'm gonna try tackling this puzzle, fuck lunch xd

(ps bump)

[mi40]

Re: The World's Hardest Sudoku (June 2012)

sudoku is rly fun

[Zapmeister]

Re: The World's Hardest Sudoku (June 2012)

one thing i like is how some random guy on the enjoy sudoku forums stumbled upon this thread earlier this year in mid-january and now it's the go-to link on the sudoku forums to point newcomers who join over there asking whether it's actually the hardest sudoku, even though these forums have nothing to do with sudoku, i hadn't posted there in over 2 years, and i don't have sources for anything

also one thing i hadn't in fact posted earlier in this thread is an actual solution path. i'll try to get that done

[mi40]

Re: The World's Hardest Sudoku (June 2012)

do you have a list of good sudokus for intermediate peeps who just bruteforce most of the time?

[igotrhythm]

Re: The World's Hardest Sudoku (June 2012)

Only that you should stay away from Wayne Gould's "fiendish" collection. I had a book of "brown belt" puzzles a while back that felt just right. Ended up solving all 300 of them.

[Zapmeister]

Re: The World's Hardest Sudoku (June 2012)

I don't know which difficulty level you're at specifically but here are a few resources

menneske.org - millions of puzzles that go from "super easy" to "impossible"
Andrew Stuart's daily sudoku - gentle/moderate/tough/diabolical/extreme
Andrew Stuart's weekly sudoku
vanhegan's sudoku site - easy to fiendish/extreme
Daily Telegraph - British right-wing newspaper that occasionally has surprisingly(!) good sudoku puzzles

As a rough difficulty guide:
menneske's "Impossible", vanhegan's "Fiendish", the Torygraph's "Diabolical" and Andrew Stuart's daily "Diabolical" are around the stage where you start branching out from pattern based techniques into chains. SE ~7
vanhegan's "Extreme" are harder but only by a little bit.
Andrew Stuart's daily "Extreme" are harder still, like SE 8+
Andrew Stuart's weekly unsolvables are entering obnoxious territory, SE 9+

igotrhythm: Wayne Gould (I think) still sticks to his 2005 mentality that sudokus should all be doable with pairs/triples and x-wings. That worked back in 2005 when they were pretty much the only techniques around, but that's no longer the case. At least you can say his puzzles don't suffer from rating inflation then. :P When did you get his book?

and finally, run like hell away from sudoku.com, the first puzzle it gave me had 15 clues and so obviously had multiple solutions

[Choofers]

Re: The World's Hardest Sudoku (June 2012)

ok so x-wing is an actual term

I learned about x-wings, y-wings, hidden/naked pairs/triples, and line-block intersection

are there otheres that I should learn about lol

[igotrhythm]

Re: The World's Hardest Sudoku (June 2012)

I don't know which difficulty level you're at specifically but here are a few resources

menneske.org - millions of puzzles that go from "super easy" to "impossible"
Andrew Stuart's daily sudoku - gentle/moderate/tough/diabolical/extreme
Andrew Stuart's weekly sudoku
vanhegan's sudoku site - easy to fiendish/extreme
Daily Telegraph - British right-wing newspaper that occasionally has surprisingly(!) good sudoku puzzles

As a rough difficulty guide:
menneske's "Impossible", vanhegan's "Fiendish", the Torygraph's "Diabolical" and Andrew Stuart's daily "Diabolical" are around the stage where you start branching out from pattern based techniques into chains. SE ~7
vanhegan's "Extreme" are harder but only by a little bit.
Andrew Stuart's daily "Extreme" are harder still, like SE 8+
Andrew Stuart's weekly unsolvables are entering obnoxious territory, SE 9+

igotrhythm: Wayne Gould (I think) still sticks to his 2005 mentality that sudokus should all be doable with pairs/triples and x-wings. That worked back in 2005 when they were pretty much the only techniques around, but that's no longer the case. At least you can say his puzzles don't suffer from rating inflation then. :P When did you get his book?

and finally, run like hell away from sudoku.com, the first puzzle it gave me had 15 clues and so obviously had multiple solutions

Not sure, but it was at least a few years ago back when there was a Borders a ways south of me on Woodward. I've only managed to solve 2 of the 200 puzzles contained therein.

I think there are 12x12 sudoku now, those are really fun.

[Zapmeister]

Re: The World's Hardest Sudoku (June 2012)

choofers: that's a pretty nice set of techniques you know already, you should be able to do basically every puzzle that has or ever will be published in a newspaper or book with what you know. if you want to learn something new, i suggest some guy's tutorial called Strong Links For Beginners which describes the technique known variously as "2 strong links", "turbot fish", "2-string kite", "skyskraper", etc. be warned that it's written in a slightly patronising way on purpose. by the way you may like to know the 3x3 extension of an x-wing is called a "swordfish"

igotrhythm: the thing is sudoku books tend not to over-reach in terms of difficulty because they're supposed to be accessible to the general public who have usually not progressed beyond all-singles puzzles, and that's to boost sales. i'd recommend you check that the puzzles actually have a unique solution before you solve them, from what you said i think it's more likely that the puzzles are flawed rather than being too hard. i may be wrong though. also i miss borders, shame about it going bankrupt

anything over 9x9 is too much damn hard work

[ReikonKeiri]

Re: The World's Hardest Sudoku (June 2012)

considering the number of clues there and this video

the "hardest puzzle" claim is fucking laughable hahaha

[qqwref]

Re: The World's Hardest Sudoku (June 2012)

"Hardest" doesn't have much to do with the number of clues. Some of the 17-clue puzzles are quite straightforward.

[Zapmeister]

Re: The World's Hardest Sudoku (June 2012)

i'm not sure what you mean by that. in general there's not really a correlation between how many clues a puzzle has and how hard they are, unless you're secretly a computer bot who only solves sudokus by brute force, in which case solving 17 clue puzzles would definitely be harder for you than (say) AAAing vertex beta vrofl or something.

hardest sudokus today typically range in the 22-24 clues region. that's just because there happen to be more minimal (i.e. you can't remove a clue and get another valid puzzle) sudokus within that clue range. in fact, some random guy did an analysis of rating over clues for minimal puzzles and they got that minimal puzzles get a little bit harder when they've got more clues. nobody knows why, though!

i have no idea how hard the hardest 17 is, but i'd be surprised if it's like a mid-9 or higher

here's a nice ridiculously hard 49 clue puzzle for your enjoyment

795|6..|8..
81.|.95|.76
.46|.87|.95
---+---+---
67.|8.9|.5.
92.|56.|78.
.58|.7.|6.9
---+---+---
56.|7..|9.8
.37|9.8|56.
.89|.56|..7

SE 10.4

[ReikonKeiri]

Re: The World's Hardest Sudoku (June 2012)

thats interesting as fuck and i didnt know that. thank you for bringing to light my ignorance