The New Sudoku Players' Forum

[dpletcher]

Here is the original puzzle from page 104 of the Tammy
Seto puzzle book. It is an Intermediate, 4 flower difficulty.

*-------+------+-----*
| . 5 . | . . . | . 2 . |
| 7 . . | . . . | . . 9 |
| . . 1 | . . . | 8 . . |
*------+------+-----*
| . . 2 | 4 5 . |1 8 7 |
| . 3 . | 6 . 1 | . 5 . |
| . . . | 7 . . | . 4 . |
*------+------+-----*
| . . . | 5 . . | . 3 . |
| 3 . . | 9 . . | 2 1 . |
| . 1 . | . . . | . . . |
*-------+------+-----*

What next step am I missing here?


*-------------------------------------------------------------------------*
| 689 5 34689 | 38 34679 46789 | 34 2 1 |
| 7 24 348 | 1 234 248 | 5 6 9 |
| 269 2469 1 | 23 23469 5 | 8 7 34 |
+---------------------------+------------------------+-------------------+
| 69 69 2 | 4 5 3 | 1 8 7 |
| 4 3 7 | 6 8 1 | 9 5 2 |
| 1 8 5 | 7 29 29 | 36 4 36 |
+---------------------------+------------------------+-------------------+
| 2689 24679 4689 | 5 1 4678 | 467 3 468 |
| 3 467 468 | 9 467 4678 | 2 1 5 |
| 5 1 468 | 238 23467 24678 | 467 9 468 |
*--------------------------------------------------------------------------*

[Ruud]

Hi dpletcher,

you must be missing that hidden triple in box 2. I sure want to tell you which digits are involved, but maybe you want to have a closer look yourself first.

Ruud.

[TKiel]

Maybe it's just me, but the naked quad in the same box was easier to spot. They both have the same end results, though.

Tracy

[MCC]

Code: Select all

*-----------------------------------------------*
|689  5     34689 |38  34679  46789 |34   2  1  |
|7    24    348   |1   234    248   |5    6  9  |
|269  2469  1     |23  23469  5     |8    7  34 |
+-----------------------------------------------+
|69   69    2     |4   5      3     |1    8  7  |
|4    3     7     |6   8      1     |9    5  2  |
|1    8     5     |7   29     29    |36   4  36 |
+-----------------------------------------------+
|2689 24679 4689  |5   1      4678  |467  3  468|
|3    467   468   |9   467    4678  |2    1  5  |
|5    1     468   |238 23467  24678 |467  9  468|
*-----------------------------------------------*

MCC

[QBasicMac]

You should get here with out too much trouble:

Code: Select all

+--------------------+-------------------+-------------+
| 689   5      34689 | 38   34679  46789 | 34   2  1   |
| 7     24     348   | 1    234    248   | 5    6  9   |
| 269   2469   1     | 23   23469  5     | 8    7  34  |
+--------------------+-------------------+-------------+
| 69    69     2     | 4    5      3     | 1    8  7   |
| 4     3      7     | 6    8      1     | 9    5  2   |
| 1     8      5     | 7    29     29    | 36   4  36  |
+--------------------+-------------------+-------------+
| 2689  24679  4689  | 5    1      4678  | 467  3  468 |
| 3     467    468   | 9    467    4678  | 2    1  5   |
| 5     1      468   | 238  23467  24678 | 467  9  468 |
+--------------------+-------------------+-------------+


Then (Ruuds hint) you notice that in Box 2 679 occurs in two cells and 69 in another. That means those three cells have 6,7, and 9 (hidden triple) and thus you can delete all other candidates from those three cells, giving

Code: Select all

+--------------------+-------------------+-------------+
| 689   5      34689 | 38   679    679   | 34   2  1   |
| 7     24     348   | 1    234    248   | 5    6  9   |
| 269   2469   1     | 23   69     5     | 8    7  34  |
+--------------------+-------------------+-------------+
| 69    69     2     | 4    5      3     | 1    8  7   |
| 4     3      7     | 6    8      1     | 9    5  2   |
| 1     8      5     | 7    29     29    | 36   4  36  |
+--------------------+-------------------+-------------+
| 2689  24679  4689  | 5    1      4678  | 467  3  468 |
| 3     467    468   | 9    467    4678  | 2    1  5   |
| 5     1      468   | 238  23467  24678 | 467  9  468 |
+--------------------+-------------------+-------------+


And now the two 4's in box 2 mean one of those cells must have a 4 (locked candidate), so you can eliminate 4's from box 1 row 2. That solves r2c2=2.

Ruud: If the op doesn't want to know, it is easy to ignore all this cryptic stuff. It is actually quite a pain to read and interpret it, so it is like secret writing. I, personally, feel free to spell out exactly to the detail how to proceed. That's what I always wanted when I came here originally and was frustrated by coy hints. Anyway, you do, of course, as you please. I am just explaining why I came after you and "gave away" the details.

Maybe the OP will correct me and say I spoiled everything. Or maybe the OP will thank me for giving actual useful help. Most likely: the OP will simply disappear, as they mostly do. Probably they lose interest.

Mac

[Cec]

Hi dpletcher,
As a follow on from Tracy's above post I too find it "easier" to spot "naked" pairs, triples or quads rather than spotting "hidden" pairs, triples or quads. In Box2, candidates [38] [234] [248] and [23] form a naked quad [2348] in this box. This means where any of these candidates occur in other cells within this box then they can be excluded from those cells. These exclusions now leave candidates [679] [679] and [69] as a "naked" triple in this group where previously these same three candidates [679] formed a "hidden" triple in this group. As Tracy points out above the end result is the same but thought I'd throw this slant in.
Cec

[absolute beginner]

the first thing i saw was the X-Wing r2r3=8=r2c8, r8c3=8=r8c6,
so eliminate the 8 from r1c3, r7c3, r9c3, r1c6, r7c6, r9c6.

But if you first see a naked quad or a x-wing -
that's personal preferance. I like to look for each digit
one by one, so x-wings are easier to me

[Cec]

"..But if you first see a naked quad or a x-wing -
that's personal preferance..."

Of course I was only comparing identification of either naked or hidden pairs, triples etc. and not comparing which of the numerous other techniques is easier to spot.

That said, I take your point that it's a personal preference which technique one looks for first and I like your choice of looking for a possible X-wing earlier in the process rather than at the end.
Cec

[QBasicMac]

Maybe the OP will correct me and say I spoiled everything. Or maybe the OP will thank me for giving actual useful help. Most likely: the OP will simply disappear, as they mostly do. Probably they lose interest.

Actually, I got a PM today (after all that time)

I appreciate your answer. I have been having trouble spotting the hidden triples and quads. I'm still working on this technique. I have solved that puzzle but now have a couple of more that I'm working on. I may request help on them shortly.
Thanks again.
Dave

Heh, I guess all people don't work on SuDoku 24/7 hence the delay.
LOL

Mac