## Stuck

Advanced methods and approaches for solving Sudoku puzzles

### Stuck

Working on an X-Tree example, I found the X-Tree and eliminated candidates. But I am still stuck.

Mac

Solution So Far
--- 13- --5
34- --5 2--
85- 9-2 ---
--- -5- 9--
--2 --- 4--
--3 -6- ---
--- -13 --6
-35 --- -1-
71- -28 ---

Pencilmarks So Far
269 2679 79 - - 467 678 4789 -
- - 1679 678 78 - - 79 179
- - 17 - 47 - 1367 347 1347
146 678 478 23478 - 147 - 23678 12378
1569 6789 - 378 789 179 - 35678 1378
1459 789 - 2478 - 1479 1578 2578 1278
249 289 489 457 - - 57 24579 -
246 - - 47 479 4679 78 - 2478
- - 469 456 - - 35 3459 349
QBasicMac

Posts: 441
Joined: 13 July 2005

Could you enlighten us on what an x-tree is. Thanks.
Jeff

Posts: 708
Joined: 01 August 2005

[quote="Jeff"]Could you enlighten us on what an x-tree is. Thanks.[/quote]

Heh - Well, I'm the one looking for help. But anyway, if you see a pattern like this

x x x x x x x x x
x x Z x x x x Z x
x x x x x x x x x

x x x x x x x x x
x x x x x x x x x
x x x x x x x x x

x x Z x x x x Z x
x x x x x x x x x
x x x x x x x x x

where there is a candidate in cells Z but not anywhere else in either the two rows or the two columns, then you have an X-Tree. That means that if the columns don't have the candidate, then you can eliminate them from the rows (and vice-versa).

Mac
QBasicMac

Posts: 441
Joined: 13 July 2005

Have a close look at row 3 - you should see an obvious placement.
SteveF

Posts: 86
Joined: 26 March 2005

QBasicMac wrote:..... if you see a pattern like this

x x x x x x x x x
x x Z x x x x Z x
x x x x x x x x x

x x x x x x x x x
x x x x x x x x x
x x x x x x x x x

x x Z x x x x Z x
x x x x x x x x x
x x x x x x x x x

where there is a candidate in cells Z but not anywhere else in either the two rows or the two columns, then you have an X-Tree. That means that if the columns don't have the candidate, then you can eliminate them from the rows (and vice-versa).

Thanks. Where did you learn the x-tree? This trick is called an x-wing in this forum.
Jeff

Posts: 708
Joined: 01 August 2005

[quote="SteveF"]Have a close look at row 3 - you should see an obvious placement.[/quote]

OK, here is row 3
- - 17 - 47 - 1367 347 1347

I have stared and see nothing.

Mac

P.S. Oops, I meant X-Wing - sorry - I don't do jargon very well.
QBasicMac

Posts: 441
Joined: 13 July 2005

QBasicMac wrote:
- - 17 - 47 - 1367 347 1347

I have stared and see nothing.

Stare a bit more. One of the candidate digits occurs only once. The jargon for that is "hidden single."
Last edited by Doyle on Mon Sep 26, 2005 4:22 pm, edited 1 time in total.
Doyle

Posts: 61
Joined: 11 July 2005

How many times do you see a 6 in row 3?
SteveF

Posts: 86
Joined: 26 March 2005

Blind spot. Otherwise I would have seen it earlier. I could have stared for a month.

I note that many of you guys at this forum are like blue-collar workers (plumbers, electricians, welders, etc.). You are cocky and cryptic with your answers. Just enough to impress your fellow workers that you know the answer, but not enough to really help the fellow in distress.

Such people love to quickly show something in a manner to make it difficult to see what happened and then sit back and laugh when the novice goofs up.

Or maybe you are a bunch of Englishmen. I have noted that they greatly fear that someone will "pick their brain". This is a concept unknown to professionals such as doctors and scientists. The professional love questions and will explain to great detail to anyone who will listen. Truly superior people.

The correct answer to my question when first posed should have been this:

"Row 3 only has one 6-candidate."

Simple, straightforward, helpful and would result in at maximum, one additional post in this thread: "Oops! Thanks!"

While I'm on my soapbox, to the fellow who asked what an X-Tree was (a thinly veiled blue-collar laugh at my goof), the proper post should have been

"I presume by X-Tree, you mean X-Wing. If not, please clarify."

That avoids my needing to explain X-Wing.

I hope this doesn't fall on arrogant, deaf ears, but instead is a word to the wise of how to really help someone.

Mac

P.S. This is not focused on the people who answered my question. It is a general observation on all answers to anyone here. Look at "Help with library puzzle Starters Hard #10". Two pages of yap. Why not simply respond with

There are candidates 56 twice in box 8. Thus the 5 in cell r9c5 can be eliminated and also the 6 in r8c5. In addition, both candidates are in row 7. Thus 5 and 6 can be eliminated from the rest of row 7, right?

This now lets us eliminate a couple of 2's in box 7 because of the two 28 pairs.

Now look at column 2. There is 28 in rows 3 and 7, thus 2 and 8 can be eliminated from the rest of column 2.

Now r5c3 is the only cell in box 4 that can be 8.

Column two has two cells with 3 and 6. Eliminate the other candidates in those two cells.

Since r5c2=36 and r5c8=36, r5c4=5 (can't be 6)

There is more, but this should get you started.
QBasicMac

Posts: 441
Joined: 13 July 2005

QBasicMac wrote:While I'm on my soapbox, to the fellow who asked what an X-Tree was (a thinly veiled blue-collar laugh at my goof), the proper post should have been

"I presume by X-Tree, you mean X-Wing. If not, please clarify."

That avoids my needing to explain X-Wing.

I hope this doesn't fall on arrogant, deaf ears, but instead is a word to the wise of how to really help someone.

Be reasonable, Mac. Only if I have a crystal ball in my pocket, then I would know your x-tree actually meant x-wing. You used the wrong term, and you expect me to figure it out in the way you have assumed. Try to put yourself into people's shoe and you will be a wiser guy. For your information, I didn't laugh until I saw your last post.

I let the others to respond to their clue given techniques or your reception ability. What on earth this has anything to do with whether you are an Englishman or not. I am an Australian, but still being criticised.
Jeff

Posts: 708
Joined: 01 August 2005

For the record, Mac, a lot of people like the cryptic clue, just a little nudge in the right direction to give them the satisfaction of solving the puzzle themselves. If it's too cryptic - ask again. You'll find a lot of threads in this forum where people have asked for help more than once, without the need of a full frontal assault on nationality or profession.
emm

Posts: 987
Joined: 02 July 2005

### Stuck

QBasicMac wrote "Hey - Well, I'm the one looking for help. But anyway, if you see a pattern like this
xxxxxxxxx
xxZxxxxZx and so on

Gee! Steady on QBasicMac - I've never heard of an x-tree either so I was glad somebody asked (politely too ). Yes, there may have been some "yap" (unnecessary talk?) in a previous thread you mentioned viz. "Help with library puzzle Starters Hard#10" - just like the first half of your above response - but both the initiator of that thread and another new member endorsed their appreciation for what they learnt.

For what it's worth, it took me a while to accept and appreciate the strange "sense of humour" behind some of the answers to questions - I later recognized this was intended to require further thought to the hint given rather than simply say "row 3 has only one 6-candidate". As I see it, this is a better way to learn.

Bonsai Cec
Cec

Posts: 1039
Joined: 16 June 2005

QBasicMac

I don't think you could be any more out of line if you tried for a month.

First -- if you want specific help, ask a specific question. Actually -- you didn't even ASK a question -- all you said is "I'm stuck". Like Jeff said, we don't have a crystal ball. We don't know if you want a hint, then next logical move, the solution -- what? Any reason you need to be so cryptic in *your* post? Why so terse? Don't want to waste electrons? And it *isn't* obvious that an x-tree = x-wing. For all we know, we missed a few posts an there's a new tactic in town. Happens every week or so.

Why not download a copy of Simple Sudoku or Sudoku Susser? They're free. They'll give as much or as little help as you'd like without an human intervention.

Though I'm not a blue collar worker -- or a Brit -- but I'll go out on a limb and say that your post is offensive to both. And to doctors and scientists as well for that matter. No one enjoys being stereotyped and pigeon holed.

I've personally been critisized for going into too much detail, not enough, giving away the answer, being to cryptic, droning on and on. If you read over a few dozen threads, I think you'll see that everyone is generally doing their best.

I mean, you didn't bother to ask for want you needed, just expected us to know what was best for you. We're not tech support. We don't work for you. Ask a specific question -- you'll be more likely to get the answer you're looking for.

You have displaced me as the author of the most obnixious post.

PS -- I think my explanation to look for several sets of naked pairs is far more help than your suggested half a page of hard to parse text. But that's just me. I wouldn't think to critisize your style when offering help to others. Reread http://forum.enjoysudoku.com/viewtopic.php?t=1674 -- no one seems to be unhappy with the discussion but you.

And would it kill you to use the CODE command on your diagrams so that those who might want to help you don't have to work so hard? Who could *possibly* parse your pencil marks? Wouldn't you rather something like this:

Code: Select all
` . . . | 1 3 . | . . 5  3 4 . | . . 5 | 2 . .  8 5 . | 9 . 2 | . . . -------+-------+------ . . . | . 5 . | 9 . .  . . 2 | . . . | 4 . .  . . 3 | . 6 . | . . . -------+-------+------ . . . | . 1 3 | . . 6  . 3 5 | . . . | . 1 .  7 1 . | . 2 8 | . . . {269}    {2679}   {679}    {1}      {3}      {467}    {678}    {46789}  {5}      {3}      {4}      {1679}   {678}    {78}     {5}      {2}      {6789}   {1789}   {8}      {5}      {167}    {9}      {47}     {2}      {1367}   {3467}   {1347}   {146}    {678}    {14678}  {23478}  {5}      {147}    {9}      {23678}  {12378}  {1569}   {6789}   {2}      {378}    {789}    {179}    {4}      {35678}  {1378}   {1459}   {789}    {3}      {2478}   {6}      {1479}   {1578}   {2578}   {1278}   {249}    {289}    {489}    {457}    {1}      {3}      {578}    {245789} {6}      {2469}   {3}      {5}      {467}    {479}    {4679}   {78}     {1}      {24789}  {7}      {1}      {469}    {456}    {2}      {8}      {35}     {3459}   {349}    `
tso

Posts: 798
Joined: 22 June 2005

I'm soooo sorry I missed this one! I think even Luna might have let me have free run at such a bigotted, arrogant and confused chappie. Such a blistering array of ignorant assumptions leave such a vast front for attack that one just doesn't know where to begin. (Sorry for using 'one' there, must remember my blue-collar roots). So I won't. Good job, everyone else.
Karyobin

Posts: 396
Joined: 18 June 2005

Sorry Mac - The Tribe has spoken!
emm

Posts: 987
Joined: 02 July 2005

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