Thousand Islands Life, Sudoku Puzzle 89, & 88 is a Doozy

Hope you are enjoying your summer and you are ready for a Sudoku challenge!

Clueless?

As a bonus each month this year we will start with a Sudoku puzzle in progress, where it appears there are no more obvious or not-so-obvious clues. Does this puzzle #88 have any more clues? If you answered “yes” you are absolutely correct.

The other day I was thinking about this puzzle, trying to find the right word to describe this clue. Somehow the word “doozy” came to mind. So, before calling this particular clue a doozy, I figured that I better check the official meaning of the word (and how to spell it). One online reference said a doozy is “Some-thing remarkable or exceptional, either positively or negatively, when compared to other in-stances of it”. How true for this clue!

Be sure to find this clue yourself, as it will become another important tool in your Sudoku bag.

(The answer follows below after the conclusion of Puzzle #89, the feature puzzle for August)

Feature Puzzle

The “Impossible” Series continues with Puzzle #89 …

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 Steps 1-8, complete the 5 Steps of Puzzle Preparation …

FILL IN DATA FROM OBSERVATIONS
FILL IN OBVIOUS ANSWERS
FILL IN NOT-SO-OBVIOUS ANSWERS
MARK UNSOLVED CELLS WITH OPTIONS THAT CANNOT EXIST IN THOSE CELLS
FILL IN THE OPTIONS FOR THE UNSOLVED CELLS

We will complete all of the first 4 steps in the order we observe them, until we conclude all Puzzle Preparation Step 1-4 clues.

The first thing we observe is that C5R6=7 & C3R7=9.

In box 9 a 1 can only exist as an option in C8R8 or C8R9; therefore, a 1 cannot exist as an option in C8R1 or C8R3. Indicate this by placing a small 1 in the bottom of those two cells.

In box 3 a 4 can only exist as an option in C7R1 or C8R1; therefore, a 4 cannot exist as an option in C1R1, C2R1 and C3R1.

In box 3 a 7 can only exist as an option in C7R3 or C8R3; therefore, a 7 cannot exist as an option in C2R3 or C3R3.

In box 7 a 3 can only exist as an option in C1R7 or C1R9; therefore, a 3 cannot exist as an option in C1R1, C1R2, C1R4 and C1R6.

In box 7 a 5 can only exist as an option in C2R8 or C3R8; therefore, a 5 cannot exist as an op-tion in C4R8, C5R8, C7R8 or C8R8.

In column 6 the options 6 & 8 can only exist in C6R3 and C6R7; so, enter those options at the top of those cells.

In box 5 a 9 can only exist as an option in C6R4 or C6R6; therefore, a 9 cannot exist as an op-tion in C6R2 and C6R9.

Now your grid should look like Example #89.1 below:

This completes puzzle preparation, so we will fill in the options for the unsolved cells, giving us Example #89.2 below:

There are no other Step 1-5 clues.

We will now proceed to Step 6: Dan’s Yes-No Challenge. We will start by searching the 1’s to see if there is a potential Step 6 clue, and then navigate through the 2-9’s.

There are 3 circumstances that establish the potential for a Step 6 exercise:

Look for just 2 unsolved cells in a box that contain the same option where these 2 cells are not in the same row or column.
Look for just 2 unsolved cells in a column that contain the same option where these 2 cells are not in the same box.
Look for just 2 unsolved cells in a row that contain the same option where these 2 cells are not in the same box.

In Example #89.3 below we will choose an 8 in C5R1 and C6R3 to perform this Step 6 exercise:

In box 2 either C5R1 or C6R3 is an 8. We will first assume C5R1 is an 8 and mark it as “Y” to indicate “yes”. We will then indicate in cells with an 8 as an option as to whether they are a yes or no. We will mark C6R3 with a small case “y” and perform the same exercise. Each of the cells with a N,n designation means that these cells cannot be an 8 regardless of whether C5R1 or C6R3 is actually an 8, and the 8 can be removed as an option from these cells, giving us Example #89.4 below:

We can clearly see that C6R7=6, C6R3=8, C7R5=8, and so forth, leading to an easy conclusion per Example #89.5 below:

May the gentle winds of Sudoku be at your back.

Dan LeKander

Clue for Puzzle #88 … focus your attention on row 9. What do you observe?
We can see that C9R9 cannot be a 5. We can see that C4R9, C5R9 & C6R9 cannot be a 5. Therefore, C1R9 or C3R9 must be a 5. This tells us that C2R8 cannot be a 5. Since the only two choices for C2R8 are a 4 or 5, we conclude C2R8=4. Then C2R7= 6, and so on.

Editor's Note: Summer 2021!

Dan, when not out fishing, and his proofreader (and, as they say, better half) Peggy, give us a new challenge each month.

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.…