## Dead in the Water...throw me a life raft

Advanced methods and approaches for solving Sudoku puzzles

### Dead in the Water...throw me a life raft

4 - - - 8 - - 6 9
- 6 3 - - - - - -
5 - 1 - 7 - - - -
7 - - 9 6 - - - 8
- - - - - 7 1 - 3
2 - - - 5 - 6 - -
1 - - - - - - - -
- 4 - - - 5 9 - -
- - - - - 8 4 3 -

OK guys, I got the 4 in the upper left hand corner, now what comes next, and WHY????? (-) is an empty box

Thanks

Steve
issac newton

Posts: 4
Joined: 11 October 2005

If you look in column 1 you'll find a hidden single. One of the digits can only go in one place in that column.
Lummox JR

Posts: 125
Joined: 22 September 2005

from another newbie, how did you get the 4 in the upper left corner? How do you know it doesn't go in r1c3 or r2c1?
Shazbot

Posts: 220
Joined: 24 September 2005

Duplicate post - Sorry - (can't find Delete key)
Last edited by QBasicMac on Thu Oct 13, 2005 1:38 pm, edited 1 time in total.
QBasicMac

Posts: 441
Joined: 13 July 2005

shazbot wrote:...how did you get the 4 in the upper left corner?

r1c1 cannot be a 1,3,5 or 6 because those values are already in box 1.
It cannot be 7,2,or 1 because those values are already in column 1.
It cannot be 8,6,or 9 because those values are already in row 1.
That leaves 4 as the only option. r1c1 MUST be 4.

issac newton wrote:... what comes next, and WHY?????

A possible next move is to note that r4c2 and r4c6 are the only cells on row 4 that contain 1 and 3. Therefore
r4c2: {135} >> {13}
r4c6: {1234} >> {13}

Also note that r2c8 and r2c9 are the only cells in box 3 that contain a 1. Therefore one of those cells MUST be 1. Therefore you can remove pencilmark 1 from 42c4,5,and 6.

By the same logic, noting r5c4 and r5c5 are the only cells in box 5 to contain a 2, r5c8: {2459} >> {459}

Also note that r1c2 and r1c3 now contain {27} each, therefore
r1c4: {1235} >> {135}
r1c6: {123} >> {13}
r1c7: {2357} >> {35}

Now r8c1=3 since it in the only pencilmark 3 in column 1.
[Above edited on 20051014. It said r9c8 before. Don't ask me why]

Note that r1c6={13}=r4c6. Therefore we can remove pencilmarks 1 and 3 from the other cells in column 6. In particular,
r6c6: {134} >> {4} <--- A solution!

After filling that in, r5c5=2 and r6c9=7

Well, try to continue from there and post back if you can't complete it.

Mac
Last edited by QBasicMac on Fri Oct 14, 2005 10:17 am, edited 1 time in total.
QBasicMac

Posts: 441
Joined: 13 July 2005

Hey Mac, I hope the swimmer wasn't submerged by that life raft you chucked over! At least you used the siphoning technique rather than the complete deluge - even if you did give it a double squirt for good measure.

Why not learn the names for these moves?
The 4 is a Naked Single
the 1,3 in row 4 are a Hidden Pair
the 1s in box 3 and the 2s in box 5 are Locked Candidates
the 2,7 in row 1 and the 1,3 in column 6 are Naked Pairs

A great site to get these sorted is http://angusj.com/sudoku/hints.php

We sound better when we're all singing from the same song sheet!
emm

Posts: 987
Joined: 02 July 2005

QBasicMac wrote:That leaves 4 as the only option. r1c1 MUST be 4.

Thanks Mac - that's such an easy one - if I'd dubbed the puzzle or printed it out and worked through it more slowly I would have probably come across it. Show you how MUCH of a newbie I am?

Em, don't worry about the terminology - I know it's nice to be all on the same page, but I still get confused with hidden single, naked single, pairs, and all that - I'd have to have gone and looked it up. Mac's explanation was perfect for me. I have that link bookmarked (but thanks anyway) and I'm still trying to s-l-o-w-l-y learn it all.
Shazbot

Posts: 220
Joined: 24 September 2005

Point taken. I guess the most important thing is that we're all harmonizing! Right?
emm

Posts: 987
Joined: 02 July 2005

em wrote:all harmonizing

LOL - A little into musical metaphors, are we?

You know, I think jargon is useful among peers. It is a nice shortcut. But, for example, in a physician-patient conversation, it would be inappropriate to use medical jargon. Always assume the patient knows none of that.

Personally, I dislike the use of jargon on this particular forum, which is found by GOOGLE by newbies struggling to solve any puzzle. I wish there were separate forums.

There would be one for geeks to exchange advanced solving techniques and discuss particular puzzle types, etc. On that forum, jargon would be the norm. Fine. I would never visit that forum personally.

There would be one for newbies to ask for next move, etc. Here, one would never see stuff such as "naked single" but would instead be told exactly what the newbie wants to know. This should be the forum at the top of GOOGLE's search for "Sudoku help".

But alas, there is only one forum. So here we are in a room with an orchestra and a rock band. harmonizing as best we can.
QBasicMac

Posts: 441
Joined: 13 July 2005

Both playing "numbers" though!
9X9

Posts: 100
Joined: 26 September 2005

### Sensi QBasicMac..thanks

You should change your name to The BIGMAC

Thanks for your time and effort in helping a newbie.

Following you advice and using your tools I solved this puzzle, and 3 more at this level.

I can not thank you enough, as I now do now have to give up Sudoku.

Thanks for everything Sensi

Issac newton
issac newton

Posts: 4
Joined: 11 October 2005

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