The New Sudoku Players' Forum

[Josh]

Hi!

I've been lurking hereabouts trying to get to grips with advanced techniques and I think I understand up to about jellyfish level...but I may be wrong.

Anyway, I'm really struggling with a puzzle that's been keeping me going on and off for a couple of days now and I'd appreciate some suggestions on how to proceed.

It started here:

Code: Select all

.2.|41.|.8.
...|.5.|9..
1.7|..8|3..
---+---+---
...|5..|.37
.6.|...|.4.
51.|..4|...
---+---+---
..5|3..|2.8
..9|.4.|...
.7.|.25|.9.



and I've got this far, which I think is all correct so far:

Code: Select all

92.|41.|.8.
...|.5.|9..
157|..8|3.4
---+---+---
.9.|5..|.37
76.|...|.4.
51.|..4|...
---+---+---
645|3..|2.8
2.9|.4.|.5.
.71|.25|49.



I solved it in desperation by guessing r9c1 (best of two eventually, after eliminations!), but there must be a logical way to do it.

Buggered if I can find it though!

Help!

Cheers!

Josh.

[CathyW]

Not sure what eliminations you've already made without your candidate list, but you have locked 3s in box 4 which gives you a single in r1c3. Then there's a couple of hidden singles.

If you post your candidate list we can see where you've got to on eliminations.

[Josh]

Oops, do you know what, I don't think I've actually eliminated anything apart from a couple in c8!

I've tried so many variations of eliminating things, I thought I'd got further than I have, sorry!

Anyway, my candidate list is:

Code: Select all

9   2  36   | 4     1     367  | 567 8  356
348 38 3468 | 267   5     2367 | 9   17 126
1   5  7    | 269   69    8    | 3   26 4
------------+------------------+------------
48  9  248  | 5     68    126  | 168 3  7
7   6  238  | 1289  389   1239 | 158 4  1259
5   1  238  | 26789 36789 4    | 68  26 2369
------------+------------------+------------
6   4  5    | 3     79    179  | 2   17 8
2   38 9    | 1678  4     167  | 167 5  136
38  7  1    | 68    2     5    | 4   9  36



Not too good eh?!

Anyway, I think the locked candidates route will be helpful so I'll try again using that technique.

Not sure how I missed that one while I was trawling for info.

Thanks for that!

Josh.

[QBasicMac]

I'd appreciate some suggestions on how to proceed.

You must have your pencilmarks wrong.

Assuming you were not using pencilmarks, but were simply solving singles, you can fill in pencilmarks now to get

Code: Select all

+---------------+--------------------+-----------------+
| 9    2   36   | 4      1      367  | 567  8     56   |
| 348  38  3468 | 267    5      2367 | 9    1267  126  |
| 1    5   7    | 269    69     8    | 3    26    4    |
+---------------+--------------------+-----------------+
| 48   9   248  | 5      68     126  | 168  3     7    |
| 7    6   238  | 1289   389    1239 | 158  4     1259 |
| 5    1   238  | 26789  36789  4    | 68   26    269  |
+---------------+--------------------+-----------------+
| 6    4   5    | 3      79     179  | 2    17    8    |
| 2    38  9    | 1678   4      167  | 167  5     136  |
| 38   7   1    | 68     2      5    | 4    9     36   |
+---------------+--------------------+-----------------+


Now you see that all the 3's in box 2 are in column 6, meaning that the 3 in column 6 MUST go in one of those two cells. So the pencilmark 3 in cell row(5) column(6) can be erased. My notation for this is:

Locked candidate 3 in box 2
Remove from r5c6

Continuing:

Locked candidate 3 in box 4
Remove from r1c3 r2c3
SOLVE: r1c3 = 6
SOLVE: r1c9 = 5
SOLVE: r1c7 = 7
SOLVE: r1c6 = 3

Locked candidate 8 in box 8
Remove from r5c4 r6c4

Now just continue with singles as you did before.

Mac

[Josh]

Hurrah!

It's the locked candidates that held the key!

Thanks CathyW and QBasicMac for the pointers.

I feel a bit of a twerp now, but at least I have another useful tool in my arsenal, even if it's a basic one that I should have been aware of already, DOH!

How chuffed am I?!

Cheers!

[QBasicMac]

Happens to us all

Mac

[Josh]

Locked candidates makes everything so much easier - wish I'd come across that sooner!

Thanks again!

[Cec]

"Locked candidates makes everything so much easier - wish I'd come across that sooner!.."

Hi Josh,
To complement Cathy's and Mac's above tips it's probably worth pointing out that all the above "Locked Candidates" examples lead to the exclusion of candidates outside a particular box in the same column. There is a variation to this technique known as "Locked Candidates 2" where candidates can be excluded from within the same box and this is best explained, along with other techniques, by clicking HERE .

Cec

[CathyW]

Locked candidates are a VERY useful technique. Cec's pointer to Angus J's site is certainly helpful - Angus offers clear descriptions of the various techniques available.

Sometimes I find I'm so intent on using a more advanced technique, such as looking for a swordfish, that I miss something more obvious. Mac is right - it happens to us all