Sudoku Puzzle #71

By: Dan LeKander

Volume 15, Issue 11, November 2020


Susie asked for an easier puzzle, so this month we will please her.  There are no advanced techniques, Steps 6-8, required, but you will need to play your “A” game to solve. [Editor's Note... Thanks Dan!]

Puzzle #71


DAN’S 8-STEP APPROACH TO SOLVING ALL SUDOKU PUZZLES

Once you have  completed the puzzle, to the extent that you have filled-in all obvious  answers and have written all potential options across the top of the  unsolved cells (PUZZLE PREPARATION), Dan recommends the following Steps  to complete the puzzle.

Step 1:  Sudoku Pairs, Triplets and Quads – See September 2015
Step 2:  Turbos & Interaction – See October 2015
Step 3:  Sudoku Gordonian Rectangles and Polygons – See November 2015
Step 4:  XY-Wings & XYZ Wings – See December 2015
Step 5:  X-Wings – See January 2016

Step 6:  DAN’S YES/NO CHALLENGE
Step 7:  DAN’S CLOSE RELATIONSHIP CHALLENGE
Step 8:  AN EXPANSION OF STEP 7Steps  1-5 are relatively common techniques and are explained in the TI LIFE  articles above. Steps 6-8 are covered in detail, in Dan’s book.


PUZZLE PREPARATION


Prior to utilizing techniques first complete the 5 Steps of Puzzle Preparation …

  1. FILL IN DATA FROM OBSERVATIONS, such as obvious pairs or triplets
  2. FILL IN OBVIOUS ANSWERS
  3. FILL IN NOT-SO-OBVIOUS ANSWERS
  4. MARK UNSOLVED CELLS WITH OPTIONS THAT CANNOT EXIST IN THOSE CELLS
  5. FILL IN THE OPTIONS FOR THE UNSOLVED CELLS

We will complete all of the first 4 steps in the order we observe them.
We will start with the 1’s and navigate through 2’s to 9’s, then repeat the process until we conclude all Puzzle Preparation Step 1-4 clues.

The first thing we observe is that C2R3 (cell in column 2, row 3) =7(obvious answer).   Then, C1R8=7.  C9R2=7.  C8R6=7.  C6R5=7.  C4R7=7.  That retires the 7’s.  C3R6=8.  C7R5=5.  C1R6=5.  C1R4=1.  C9R6=1.

In box 5 the only cells that could have a 2 as an option are C4R4 or C6R4; therefore, a 2 cannot exist as an option in C7R4-6.  Therefore, C9R5=2.

In box 3 the only cells that can have a 3 as an option are C8R1 or C9R1; therefore, a 3 cannot exist an option in C1R1, C2R1 or C3R1.  Therefore, C3R2=3.

In column 1 a 2 cannot exist as an option in C1R5 or C1R9; therefore, C1R1=2. The options for C7R4, C8R4 and C9R4 are limited to 469, an obvious triplet. The options for C7R8 & C9R8 are 68, an obvious pair. The options for C4R9 & C6R9 are 68, an obvious pair. The options for C4R6, C5R6 & C6R6 are 469.

The options for C4R4, C6R4 and C5R5 are limited to 238.  There is already a 28 in row 5; therefore, C5R5=3. C4R8=3. The options for C4R4 & C6R4 are now 28
C2R4=3.

The options for C1R5, C2R5 & C3R5 are limited to 469.  There is already a 4 and 6 in column 1; therefore, C1R5=9.  C1R9=3. The options for C2R5 & C3R5 are 46.
In box 2 a 5 must exist in C4R1-3; therefore, a 5 cannot exist as an option in C6R1 or C6R2.  Given that, the only cell in row 2 that can be a 5 is C4R2.  C4R2=5.

That wraps up Puzzle Preparation steps 1-4, so now your grid should look like Example #71.1 below:

Example #71.1

That wraps up Puzzle Preparation steps 1-4, so it is time to complete step 5 by filling in the options for the remaining unsolved cells.   Now your grid should look like Example #71.2 below:

Example #71.2

TECHNIQUES STEPS 1-5

In column 5 the three cells C5R2,7,8 have options 149, an obvious triplet; therefore, the other unsolved cells in column 5 cannot have options 149.  Then, C5R6=6 and C5R3=8.  C9R3=9.

Now, either C5R2 or C6R2 must be a 9; therefore, you can remove the 9 as an option for C4R1 & C6R1.

Now your grid should look like Example #71.3 below:

Example #71.3

At this point we have created an obvious triplet.   Can you spot it?

In column 4 we have three cells that share 3 options … C4R3, C4R4 & C4R9 share options 268, so we can remove those options from the other unsolved cells in column 4.  C4R1=4.  C4R6=9, and so forth, leading to an easy solution per Example #71.4 below:

Example #71.4

We all learned from this puzzle how important it is to revisit common techniques after we have made changes to a puzzle.  Hope you have enjoyed this puzzle.

May the gentle winds of Sudoku be at your back.

Dan LeKander

____________________________________

Editor's Note:  Again, I want to thank Dan…and his proofreader… Peggy!  I wrote last month that this editor can find 1001 reasons to do something other than dusting... so I know how hard it is to actually buckle down and not go fishing unless you have closed up and headed to the winter digs... So thank you Mr. and Mrs. LeKander - we have come a long from from 2016!

It was back in January 2016, when we published a final article in Dan's Series of Steps to learn the logic of Sudoku –  he asked if we would like a puzzle to solve every month … this editor said an enthusiastic… Yes, please!

If you have not already done so, I suggest you purchase Dan’s book: “3 Advanced Sudoku Techniques, That Will Change Your Game Forever!” Purchase of a book includes a 50-page blank grid pad, 33 black and two green tokens, to assist with Step 6.…

I also encourage you to write to Dan and tell him how his system is helpful!

The book is available online at ebay.com.

Most importantly, I ask that you leave comments on any part of his series and throughout the year.

Be sure to read the TI Life's review of Dan's book by Jesse Kahn published in Jun 2015.

Here are links to all past Sudoku Puzzle Challenge beginning: February 2016, March 2016, April 2016, May 2016, June 2016, July 2016, August 2016, September 2016, October 2016, November 2016, December 2016, January 2017, February 2017, March 2017, April 2017, May 2017, June 2017, July 2017, August 2017, September 2017, October 2017, November 2017, December 2017, January 2018, February 2018, March 2018, April 2018, May 2018, June 2018, July 2018, August 2018, September 2018, October 2018, November 2018, December 2018, January 2019, February 2019, March 2019, April 2019, May 2019, June 2019, July 2019, August 2019, September 2019, October 2019, November 2019, December 2019, January 2020, February 2020, April 2020, May 2020,  June 2020 and July 2020, August 2020,  September 2020 and October 2020.

Posted in: Volume 15, Issue 11, November 2020, Sports, Current



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