The New Sudoku Players' Forum

[SuDokuKid]

I'm totally stuck!

Rating 5/5

6,5,28 | 7,4,3 | 1289,89,189
48,14,1348 | 2,9,6 | 5,348,7
9,7,234 | 15,8,15 | 24,6,34

1,24,458 | 56,267,9 | 3,458,468
2478, 9,458 | 356,2367,245 | 4678,1,468
47,3,6 | 8,17,145 | 479,59,2

24,8,149 | 136,1236,12 | 1469,7,5
5,1246,7 | 9,126,8 | 146,34,1346
3,16,19 | 4,5,7 | 1689,2,1689

Bold are the Hints. As you can see I didn't get very far.

[Shazbot]

You have a hidden single in row 4, but you can do some eliminations BEFORE you place that one...

You can remove 2s from r5c5 and r7c5 using an Xwing on rows 5 and 7, columns 1 and 6. Then use that hidden single. This will give you another hidden single in column 5.

See how far that gets you....

Edit: quoted the wrong rows/columns for the xwing - sorry

[r.e.s.]

Would anyone care to check what difficulty-rating Pappocom's software gives to this non-Pappocom sudoku? (I'm just curious.) Here's the puzzle in easier-to-read format ...

Code: Select all

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

Edit: the clues in boxes 3 and 7 are symmetrical, but it isn't clear from the puzzle, as posted, whether there are 2 clues (or 3) in each. I'm guessing there are a total number of 28 (rather than 30) clues.

[Shazbot]

Pappocom rates it Hard. The 5 in box 7 wasn't in the original puzzle.

[r.e.s.]

Pappocom rates it Hard.

Thanks ... there seems to be a problem with the clues that SuDokuKid gave for boxes 3 and 7 (they were symmetrical in the newspaper as I recall). Maybe it doesn't affect the rating though.

PS: This one was rated *diabolical* (!) in the L.A. Times.

[Shazbot]

You're right - even with the 5 provided, it's still rated by Pappocom as Hard. I hadn't noticed the lack of symmetry.

[SuDokuKid]

Sorry. The 7 in box 3 should not be a clue.

[SuDokuKid]

I started over and can't figure out how I got the 3 in box 4 now!!!

I can't see the XWING as indicated hence I can't find the hidden singles. Can someone explain that?

I do see the 7 as the hidden single in r4C5 but don't understand the xwing.

[emm]

Sudoku Susser solves the 28 clue version with nothing more than one naked pair, one locked candidates and 50+ hidden and naked singles - I stopped counting. Doesn't sound like a Hard / Diabolical.

[Shazbot]

Even without the 7 in box 3, Pappocom still rates this puzzle as hard.

I can't see the XWING as indicated hence I can't find the hidden singles. Can someone explain that?

Em's right - you probably don't need the xwing at all, but I noticed the xwing before I placed the hidden single in r4c5 so thought I'd take advantage of it. So it's not necessary, but seeing as you asked...

Numbers in bold indicate the x-wing. Numbers in red (italics didn't show very well) are those that can be eliminated because of it.

Code: Select all

 *-----------*
 |65.|743|...|
 |...|296|5.7|
 |97.|.8.|.6.|
 |---+---+---|
 |1..|..9|3..|
 |.9.|...|.1.|
 |..6|8..|..2|
 |---+---+---|
 |.8.|...|.75|
 |5.7|9.8|...|
 |3..|457|.2.|
 *-----------*

 *--------------------------------------------------------------------*
 | 6      5      128    | 7      4      3      | 1289   89     189    |
 | 48     134    1348   | 2      9      6      | 5      348    7      |
 | 9      7      234    | 15     8      15     | 24     6      34     |
 |----------------------+----------------------+----------------------|
 | 1      24     2458   | 56     267    9      | 3      458    468    |
 | 2478   9      23458  | 356    2367   245    | 4678   1      468    |
 | 47     34     6      | 8      137    145    | 479    459    2      |
 |----------------------+----------------------+----------------------|
 | 24     8      1249   | 136    1236   12     | 1469   7      5      |
 | 5      1246   7      | 9      1236   8      | 146    34     1346   |
 | 3      16     19     | 4      5      7      | 1689   2      1689   |
 *--------------------------------------------------------------------*


Row 5: 2478 9 23458 | 356 2367 245 | 4678 1 468 |
Row 7: 24 8 1249 | 136 1236 12 | 1469 7 5 |

Which leaves you with

Code: Select all

 *-----------------------------------------------------------*
 | 6     5     128   | 7     4     3     | 1289  89    189   |
 | 48    134   1348  | 2     9     6     | 5     348   7     |
 | 9     7     234   | 15    8     15    | 24    6     34    |
 |-------------------+-------------------+-------------------|
 | 1     24    2458  | 56    267   9     | 3     458   468   |
 | 2478  9     3458  | 356   367   245   | 4678  1     468   |
 | 47    34    6     | 8     137   145   | 479   459   2     |
 |-------------------+-------------------+-------------------|
 | 24    8     149   | 136   136   12    | 1469  7     5     |
 | 5     1246  7     | 9     1236  8     | 146   34    1346  |
 | 3     16    19    | 4     5     7     | 1689  2     1689  |
 *-----------------------------------------------------------*


After you place the 7 in r4c5, there's only one place for the 2 to go in c5.

[emm]

I think there's too many 2s for an Xwing in r48c25. I can see a couple of others there though.

[Shazbot]

You need to search the COLUMNS for the xwing, not the ROWS (I find this really difficult to do - you've almost got to turn your head sideways!). Columns 1 and 6 each contain only two 2s, and they share the same rows - 5 and 7. Therefore any remaining candidate 2s in rows 5 and 7 can be removed (excluding those in columns 1 and 6).

Oops - sorry - I see I gave you ENTIRELY the wrong columns and rows in my first post (which I've now edited), but gave the correct ones in my more lengthy explanation. Why do I keep tripping up like that?

[9X9]

Keep off the "Fosters" Shazzer!

[Shazbot]

ah, the cat's out of the bag - you got me!

[SuDokuKid]

Thanks Shazbot!

To be honest, you're explanation of the X-Wing was the best I've read so far. It triggered something in my brain that finally... FINALLY made sense!