## help with a demanding Will Shortz puzzle

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### help with a demanding Will Shortz puzzle

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  12792   9  6 | 3     7     14 | 84     5     8147  1  8 | 49    5     249| 6      2479  3---------+----------------+-----------------5   8  47| 2     6     479| 1      3     7919  2  3 | 1479  149   8  | 479    6     519  6  47| 5     149   3  | 2479   8     279---------+----------------+-----------------36  5  2 | 1697  189   179| 3789   179   48   7  9 | 14    3     124| 5      12    636  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
pdxdavej

Posts: 2
Joined: 05 March 2008

### Re: help with a demanding Will Shortz puzzle

pdxdavej wrote: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  12792   9  6 | 3     7     14 | 8-4     5     8147  1  8 | 49    5     249|  6      2479  3---------+----------------+-------------------5   8  47| 2     6     479|  1      3     7919  2  3 | 1479  149   8  | *479    6     519  6  47| 5     149   3  | *2479   8     279---------+----------------+-------------------36  5  2 | 1697  189   179|  3789   179   48   7  9 | 14    3     124|  5      12    636  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.
hobiwan
2012 Supporter

Posts: 321
Joined: 16 January 2008
Location: Klagenfurt

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
pdxdavej

Posts: 2
Joined: 05 March 2008

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