Sudoku Puzzles 119, 120 & 121

By: Dan LeKander

Volume 17, Issue 9, September 2022

We continue with 3 puzzles each month.   Something for everyone!

Clueless?

We start with a Sudoku puzzle in progress, where it appears that there are no more obvious or not-so-obvious clues.  Can you find the hidden clue in Puzzle #119?

PUZZLE #119

(The answer follows the conclusion of Puzzle #121, the feature puzzle for September)

Logic Puzzle

Difficult rating … 5/10
(Rating based on puzzles not requiring advanced techniques)

Puzzle #120 should present a moderate challenge!

Puzzle #120

Feature Puzzle

Difficult rating …  7/10
(Rating based on puzzles requiring advanced techniques)

Puzzle #121

PUZZLE PREPARATION

Prior to utilizing techniques 1-8, complete the 5 Steps of Puzzle Preparation …

  1. FILL IN DATA FROM OBSERVATIONS
  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

The first thing we observe is that C4R7=2 & C7R6=9.

The only unsolved cell in row 5 that could be a 6 is C3R5.  C3R5=6.  Then, C2R7=6.

The only unsolved cell in row 5 that could be a 7 is C5R5.   C5R5=7.  Then, C1R5=4.

In column 6, C6R4, C6R7, C6R8 & C6R9 can only have options 3, 7, 8 & 9.  This leaves C6R2, C6R3 & C6R6 limited to options 4, 5 & 6.

C8R4 & C8R6 have options 1 & 5.  C7R4, C7R5 & C7R6 can only have options 2, 3 & 8.

In row 1 C4R1 & C7R1 can only have options 6 & 7.

In box eight, a 1 can only exist as an option in C4R8 & C5R8; therefore, a 1 cannot exist as an option in C1R8, C3R8, C7R8, C8R8 & C9R8.

In box one, a 2 can only exist as an option in C3R2 & C3R3; therefore, a 2 cannot exist as an option in C3R4 & C3R6.

Now your grid should look like Example #121.1 below:

Example #121.1

This completes Puzzle Preparation Steps 1-4.  Next, we will fill in options for all unsolved cells, giving us Example #121.2 below:

Example #121.2

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 7. Steps  1-5 are relatively common techniques and are explained in the TI LIFE articles. Steps 6-8 are covered in detail, in Dan’s book.


There are no Step 1-5 techniques that can be further applied.  Are there are any good Step 6 potentials.  As in previous articles, we determined a particular number was a potential for a successful Step 6 exercise if that number appears as a given answer in 3 separate boxes, such that the boxes are not side-by-side, nor over each other.  Which numbers do you see that are good candidates?   Yes, the 7’s, however the Step 6 exercise does not produce any clues, so we will move on to Step 7, Dan’s Close Relationship Challenge.

We will pick C6R2 as our starter cell, with a sequence of 5,6.   We will annotate this on the 2nd level of this cell, as per Example #121.3 below:

Example #121.3

So, why did I pick as a starter cell C6R2 with a sequence 5,6?

By selecting C6R2 with the sequence 5,6, we would have immediate answers for C6R6 &C6R3, C4R1,as well as C8R2.   This almost guarantees that the 6 will track through the puzzle far enough to give us positive results.

We annotate C3R2, C6R3, C7R2 & C9R2 with N5 indicating that those cells cannot be a 5 if the starting cell is a 5.  As we track the 6 through the puzzle, if any of these cells is a value other than 5, it would indicate that this cell is not a 5 regardless if the starter cell is a 5 or 6, and the 5 could be deleted as an option for that cell.

Before we perform this exercise, we will list the potential outcomes …

• The tracking of the second number of the starter cell doesn’t reach the N9 cells, and therefore, the exercise is unsuccessful.

• The tracking of the second number goes entirely through the puzzle without a conflict, indicating that the 2nd number is correct for the starter cell and you have solved the puzzle.

• The tracking of the second number creates a conflict, such as a number showing up twice in a row, column or box.   Or it could show up by having no cell for a particular number in a row, column or box. Regardless of how the conflict arises, it would mean the second number is incorrect for that cell, and therefore, the answer to the starter cell is the first number.

Example 121.4

We will now track the 6 through the puzzle above on the third level of the unsolved cells to preserve the integrity of the original puzzle.

As you can see from the example above, in tracking the 6 through the puzzle, we have two 2’s in column 8.   This is a conflict!   Therefore, C6R2 cannot be a 6.   We have now determined that C6R2=5.

The puzzle is easily solved from this point, giving us Example #121.5 below:

Example #121.5

May the gentle winds of Sudoku be at your back.

Dan LeKander


Clue for Puzzle #119 …  did you find the clue?  If not, read on.

• Check row 7.  What do you see?

• We see that C1R7 & C4R7 have options 2 & 7.  Then, C3R7=4.  You may want to continue and see if you can solve the puzzle!


Editor's Note:  Note: we went into the 100s in May 2022

Now here are Puzzles #119, #120, & #121

"I keep saying . . . when we published the final article in Dan's Series of steps to learn the logic of Sudoku, I never in a zillion years thought that Dan would so graciously offer to do one or two puzzles for us each month - and he has done so without my asking. Now we are up to 3!

Then his wife, Peggy, does the proof reading and I only have to post in on TI Life. We would love to know how many you have solved.  (Many, darn it, have stumped me, but I look forward to them each month.)

In May someone wrote to ask how to fill them out online. Unfortunately, you need to print them yourself - but that is easy to do and I know you will have just as much fun.

And, 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. The book is available by contacting info@thousandislandslife.com.

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, October 2020, November 2020 and December 2020, January 2021, February 2021, March 2021, April 2021, May 2021, June 2021, July 2021 , August 2021, September 2021 ,  October 2021, November 2021, December 2021, January 2022, February 2022, March 2022, April 2022 , May 2022, June 2022, July 2022 and August 2022.

Posted in: Volume 17, Issue 9, September 2022, Sports


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