The New Sudoku Players' Forum

[pdxdavej]

Book: Will Shortz presents sudoku for 365 days.
Puzzles by pzzl.com

Puzzle # 221 (Demanding)

Starting grid:

Code: Select all

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

With my pencil marks:

Code: Select all

47  3  5 | 8     1249  6  | 2479   2479  1279
2   9  6 | 3     7     14 | 84     5     81
47  1  8 | 49    5     249| 6      2479  3
---------+----------------+-----------------
5   8  47| 2     6     479| 1      3     79
19  2  3 | 1479  149   8  | 479    6     5
19  6  47| 5     149   3  | 2479   8     279
---------+----------------+-----------------
36  5  2 | 1697  189   179| 3789   179   4
8   7  9 | 14    3     124| 5      12    6
36  4  1 | 679   289   5  | 23789  279   2789
---------+----------------+-----------------

Now I’m stumped. I would appreciate learning the next step for this puzzle and the logic behind that step.

Dave J

[hobiwan]

Now I’m stumped. I would appreciate learning the next step for this puzzle and the logic behind that step.

Code: Select all

47  3  5 | 8     1249  6  | 2-479   2479  1279
2   9  6 | 3     7     14 | 8-4     5     81
47  1  8 | 49    5     249|  6      2479  3
---------+----------------+-------------------
5   8  47| 2     6     479|  1      3     79
19  2  3 | 1479  149   8  | *479    6     5
19  6  47| 5     149   3  | *2479   8     279
---------+----------------+-------------------
36  5  2 | 1697  189   179|  3789   179   4
8   7  9 | 14    3     124|  5      12    6
36  4  1 | 679   289   5  |  23789  279   2789
---------+----------------+-------------------

Look at block 6: It has only two candidates left for digit 4 and both candidates are in column 7. Since one of these candidates has to be set, all candidates for digit 4 in column 7 outside block 6 can be eliminated. This move is called "Locked Candidates Type 1" or "Pointing". After that it's all singles.

If you are interested in solving techniques I suggest looking at Sudopedia.

[pdxdavej]

Thanks! I didn't see the pointing because there were so many possibilities in each square. I got hung up looking for more complex relationships, now I know to go back to basics when I get stuck.

Thanks for the help. Dave J