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Sudoku Puzzle Challenge-October 2016


Fall is upon us. Give yourself a lift & solve both Sudoku puzzles this month!

First, we will revisit the approach as discussed in Dan’s first six TI LIFE articles …

 

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.

See TI Life Puzzle Preparation:

Step 1:  Sudoku Pairs, Triplets and Quads – September, 2015

Step 2:  Turbos & Interaction – October, 2015

Step 3:  Sudoku Gordonian Rectangles and Polygons – November, 2015

Step 4:  XY-Wings & XYZ Wings – December, 2015

Step 5:  X-Wings – 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 per above. Steps 6-8 are covered in detail, in Dan’s book.

Also see Sudoku Puzzle Challenge… February 2016, Sudoku Puzzle Challenge–March 2016, Sudoku Puzzle Challenge–April 2016, May 2016, June 2016, July 2016, August 2016 and September 2016.

PUzzle 17 Dan

Puzzle #17

Puzzle #17 can be solved with Steps 1-5. I would give this puzzle a rating of 7/10 (with 10 being the most difficult) for puzzles not requiring advanced techniques.

If you need assistance, Puzzle Preparation should result in the puzzle looking like below:

Puzzle 17 prep

Puzzle #17: Through Puzzle Preparation

The Puzzle Preparation above is influenced by two observations. First, there is an obvious pair in row four. C4R4 (cell in column 4, row 4) & C9R4 both have options 7, 9 which is an obvious pair, eliminating 7 & 9 from any other cells in row 4. Secondly, in box #1: C1R1, C1R2, C2R1 & C3R1 cannot be a 1 or 5. Therefore the only choices for a 1 and 5, in box #1, are the two cells, C2R2 & C3R3. Therefore, their options must only be 1 & 5.

HINT: when doing your Puzzle Preparation it is important to discover what options cannot exist in cells.

Steps to completeting Puzzle #17

Step 2 … C1R1 & C3R1 form an Interaction, eliminating the 4, in C5R1. Then C7R1=3 & C4R2=3.

Step 2 … C1R1, C2R1 & C3R1 form an Interaction, eliminating the 7, from C5R1.

Step 2 … C1R1 & C1R2 form an Interaction, eliminating the 8, from C2R1 & C3R1.

(note … the first three clues all result from activity in box #1!)

Step 1 … C2R1 & C2R8 is an obvious pair 2,7, eliminating the 2 & 7 from the other cells, in column 2.

Step 2 … C1R6 & C3R6 form an Interaction, eliminating a 7, from Cells C1R5 & C3R5.

Step 2 … C1R5 & C1R6 form an Interaction, eliminating the 9, from C3R5 & C3R6.

Step 2 … C8R9 & C9R9 form an Interaction, eliminating the 3, from C5R9. Then C5R7=3.

Step 2 … C4R4 & C5R5 form a Turbo, eliminating the 9, from C9R9.

Step 3 … C1R1, C2R1, C1R8 & C2R8 form a Gordonian Rectangle Plus, eliminating the 2 & 7, from C1R1.

Step 5 … C4R4, C9R4, C4R8 & C9R8 form an X-Wing, eliminating the 9, from C4R7, C9R2 & C9R5. Then C9R2=1.

From this point, the puzzle is easily solved.

Puzzle 17 complete
Puzzle #17 Complete

PUZZLE #18 … difficulty rating 2/10 for puzzles requiring advanced techniques.

Puzzle 18

Puzzle #18

Hints … what are the only two possible options for C1R7 & C2R8? What are the only two cells in box #5 that can have options 23?

If you need assistance, Puzzle Preparation should result in the puzzle looking like below:

PUzzle 18 Prep
Puzzle #18 Through Puzzle Preparation

Steps to completing Puzzle #18

In the Puzzle Preparation Phase it is important to note that options 1 & 6 can only exist in C1R7 & C2R8. Therefore no other options can exist in those two cells. (This is the same scenario as in Puzzle #17).

Step 1 … C9R7 & C9R8 form an Interaction, eliminating the 1 from C9R6, C9R3 & C9R1.

Step 2 … C3R6 & C9R6 form a pair 45, eliminating the 4 & 5 from the other unsolved cells in row 6.

Step 3 … C2R6 & C2R8 form a pair 16, eliminating the 1 & 6 from the other cells in column 2. Then C2R4=9, C5R4=7, C5R5=9 & C7R5=7.

Step 4 … C2R1 & C2R9 form a Step 6 “Dan’s Yes No Challenge, eliminating the 5 from C9R1 & C7R9.

Step 5 … C3R6 & C9R6 form a Step 6, eliminating the 5 from C4R9.

Step 6 … we will select C2R9 to do a “Dan’s Close Relationship Challenge” with the sequence 5,4. (If C2R9 is a 5, then C1R9, C3R7 & C8R9 can be marked with a n9, indicating that if C2R9 is a 5, then those 3 cells cannot be a 5. Next we assume C2R9 is a 4 and track the 4 through the puzzle. Then C2R1=5, C1R2=3, C1R3=9. Then C1R9=5. So what have we learned? Well, if C2R9 is a 4, then C1R9 is a 5. Then C3R7 & C8R9 are not a 5. So regardless if C2R9 is a 5 or 4, C3R7 & C8R9 are not a 5, and the 5 can be eliminated from those two cells.) Then C3R7=9, and from this point the puzzle can be easily solved.

Puzzle 18 complete

Puzzle #18 Complete

Editor’s note:

Do you tackle a Sudoku on your cottage veranda, sailboat cockpit, or at a campsite?  TI Life is taking full advantage of Dan LeKander, from Wellesley Island, who is a Sudoku expert and author of “3 Advanced Sudoku Techniques – That Will Change Your Game Forever!”

In January 2016, we published a final article in his series – but many of us enjoy using “Dan’s Steps,” so when he asked if we would like a puzzle to solve every month … this editor said an enthusiastic… Yes, please!

I suggest you try this relatively easy puzzle and that you also purchase Dan’s book, “3 Advanced Sudoku Techniques, That Will Change Your Game Forever!”

Most importantly, I ask that you leave comments on any part of his series and throughout the coming year.  Remember when your teacher said –  no such thing as a silly question – as we can all learn together.

Dan’s book is available at two locations online, djlsuniverse.com, amazon.com and on ebay.com.

Purchase of a book includes a 50-page blank grid pad, 33 black and two green tokens, to assist with Step 6.…

I want to thank Dan… what a lot of work he puts into our TI Life articles.  And another thank you goes to Bill Stallan, who proofreads the content each month!)

Do you have any suggestions for future articles? You can post on this TI Life issue, or contact me directly at my e-mail address … djlsuniverse@yahoo.com.

Thank you for your interest. May the gentle winds of Sudoku be at your back!

Dan LeKander

Dan LeKander and his wife, Peggy, have been seasonal residents of Fineview, on Wellesley Island, NY, since 1983.  In addition to being a Sudoku addict, Dan explores the 1000 Islands, to enjoy the wildlife, beauty and of course, Catch-and Release bass fishing.

[See Jessy Kahn’s Book Review, “3 Advanced Sudoku Techniques…” by Dan LeKander, June issue of TI Life.]

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