The New Sudoku Players' Forum

[Suzie2kids]

Hi - I caught the Sudoku bug last Tuesday and have solved several at this point. The puzzle below is from The Journal News (a Gannett paper in the US). It is ranked 5 stars out of 5 stars (therefore, I assume, hard).

I've entered the puzzle below. I use "-" to indicate a change in cells. I had difficulty in entering the puzzle in a legible way.

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

I've spent quite a bit of time on it - at one point completely erasing all my entries and then re-starting. I'm enjoying the challenge.

I don't want the answer, but I'd love to be told whether I should employ certain techniques (x-wing, swordfish, etc.). I'm trying to understand the logic behind the techniques, so by struggling through it myself I'm hoping to become adept at recognizing the situations that they should be utilized.

Thanks!

[Suzie2kids]

Well, I finally got it. Though, I can't recall what tripped me over the edge to finally "getting it". Also, I can't tell what techniques I used. It just flowed after a while. No guessing. I'm looking forward to solving more! I've got another one, also a 5 out of 5 (from Sunday's puzzle).

[tarek]

hi there Suzie2kids,

I'm not sure what techniques did u use to reach the position u pencilmarked above.

How did eliminate candidates in r2c9 for example.
There is also a naked single (1) in column 5 that u missed.

It can be difficult to assist you without the original puzzle & more difficult when you post your pencilmarks as you did.

replacing your multiple candidate cells with blanks, my solver did't reach reach the same conclusion that you have (I assume that you may have used some advanced technique because you caught the BUG ). but then again there are a few box line interactions which you missed.

This is how my solver sees it & solves it.

Code: Select all

*-----------------------------------------------------------------*
| 124    7      46    | 9      3      126   | 8      5      12    |
| 9      1234   5     | 28     278    126   | 1347   13467  1237  |
| 8      123    36    | 4      257    1256  | 9      1367   1237  |
|---------------------+---------------------+---------------------|
| 234    2349   1     | 7      259    235   | 34     8      6     |
| 5      8      37    | 1      6      4     | 37     2      9     |
| 6      2349   347   | 23     29     8     | 5      1347   137   |
|---------------------+---------------------+---------------------|
| 347    34     8     | 6      1      9     | 2      37     5     |
| 137    5      9     | 238    28     23    | 6      137    4     |
| 13     6      2     | 5      4      7     | 13     9      8     |
*-----------------------------------------------------------------*
Eliminating 1 From r1c1 (Column 2 & Box 1 Box-line interaction)
*-----------------------------------------------------------------*
| 24     7      46    | 9      3      126   | 8      5      12    |
| 9      1234   5     | 28     278    126   | 1347   13467  1237  |
| 8      123    36    | 4      257    1256  | 9      1367   1237  |
|---------------------+---------------------+---------------------|
| 234    2349   1     | 7      259    235   | 34     8      6     |
| 5      8      37    | 1      6      4     | 37     2      9     |
| 6      2349   347   | 23     29     8     | 5      1347   137   |
|---------------------+---------------------+---------------------|
| 347    34     8     | 6      1      9     | 2      37     5     |
| 137    5      9     | 238    28     23    | 6      137    4     |
| 13     6      2     | 5      4      7     | 13     9      8     |
*-----------------------------------------------------------------*
Eliminating 4 From r2c2 (Row 1 & Box 1 Box-line interaction)
*-----------------------------------------------------------------*
| 24     7      46    | 9      3      126   | 8      5      12    |
| 9      123    5     | 28     278    126   | 1347   13467  1237  |
| 8      123    36    | 4      257    1256  | 9      1367   1237  |
|---------------------+---------------------+---------------------|
| 234    2349   1     | 7      259    235   | 34     8      6     |
| 5      8      37    | 1      6      4     | 37     2      9     |
| 6      2349   347   | 23     29     8     | 5      1347   137   |
|---------------------+---------------------+---------------------|
| 347    34     8     | 6      1      9     | 2      37     5     |
| 137    5      9     | 238    28     23    | 6      137    4     |
| 13     6      2     | 5      4      7     | 13     9      8     |
*-----------------------------------------------------------------*
Eliminating 3 From r8c1 (Box 8 & Row 8 Box-Line interaction)
Eliminating 3 From r8c8 (Box 8 & Row 8 Box-Line interaction)
*-----------------------------------------------------------------*
| 24     7      46    | 9      3      126   | 8      5      12    |
| 9      123    5     | 28     278    126   | 1347   13467  1237  |
| 8      123    36    | 4      257    1256  | 9      1367   1237  |
|---------------------+---------------------+---------------------|
| 234    2349   1     | 7      259    235   | 34     8      6     |
| 5      8      37    | 1      6      4     | 37     2      9     |
| 6      2349   347   | 23     29     8     | 5      1347   137   |
|---------------------+---------------------+---------------------|
| 347    34     8     | 6      1      9     | 2      37     5     |
| 17     5      9     | 238    28     23    | 6      17     4     |
| 13     6      2     | 5      4      7     | 13     9      8     |
*-----------------------------------------------------------------*
Eliminating 7 From r2c8 (Box 9 & Column 8 Box-Line interaction)
Eliminating 7 From r3c8 (Box 9 & Column 8 Box-Line interaction)
Eliminating 7 From r6c8 (Box 9 & Column 8 Box-Line interaction)
*--------------------------------------------------------*
| 24    7     46   | 9     3     126  | 8     5     12   |
| 9     123   5    | 28    278   126  | 1347  1346  1237 |
| 8     123   36   | 4     257   1256 | 9     136   1237 |
|------------------+------------------+------------------|
| 234   2349  1    | 7     259   235  | 34    8     6    |
| 5     8     37   | 1     6     4    | 37    2     9    |
| 6     2349  347  | 23    29    8    | 5     134   137  |
|------------------+------------------+------------------|
| 347   34    8    | 6     1     9    | 2     37    5    |
| 17    5     9    | 238   28    23   | 6     17    4    |
| 13    6     2    | 5     4     7    | 13    9     8    |
*--------------------------------------------------------*
Candidates in r3c8 will force r4c7 to have only 4 as valid Candidates
r3c8=1: r3c8=1 => r1c9=2 => r1c1=4 => r1c3=6 => r3c3=3 => r5c3=7 => r5c7=3 => r4c7=4
r3c8=3: r3c8=3 => r7c8=7 => r8c8=1 => r9c7=3 => r4c7=4
r3c8=6: r3c8=6 => r3c3=3 => r5c3=7 => r5c7=3 => r4c7=4
Threfore r4c7=4


it's easy from here

Tarek