Sudoku Puzzle Challenge–June 2016

The Sudoku puzzles in this June issue of Thousand Island Life may be the most challenging yet!

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 … 2015 TI LIFE ARTICLE PUZZLE PREPARATION AUGUST 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

PUZZLE # 9

In keeping with the theme of the last 3 months, puzzle #9 can be solved with Steps 1-5, and puzzle #10 will require Step 6 assistance. Please remember to process obvious pairs in the puzzle preparation phase (hint …check rows 3 & 9).

Puzzle # 9 Preparation

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

Puzzle # 9  Preparation

If your puzzle does not look like the one above, you probably missed something in Puzzle Preparation. For example, there is an obvious pair in row three; cells C2R3 (column 2, row 3) and C6R3 both have “47” as options. Therefore C3R3 = 2 and cells C4R3 and C7R3 now both have “59” as options. Plus, C3R3 being a 2 highly changes the options of the other unsolved cells in box 4. Row 9 has another obvious pair; both C2R9 and C9R9 have “17” as options. Therefore C8R9 = 5 and then C1R9 = 9.

Steps to complete Puzzle #9 …

Step 1 (pairs, triplets, & quads) …

· In row 4, four cells exclusively have the options 2, 6, 8 & 9 (R1R4, C2R4, C4R4 & C6R4). This is a quad. Options 2, 6, 8 & 9 can therefore be eliminated from C3R4, C7R4 and C8R4. C3R4 remains with option 17. C7R4 now has option 14 and C8R4 has options 147.

· In Step 1 above, C7R4 now has option 14. C7R7 also has option 14. Therefore this pair in column 7 eliminates a 1 from cell C7R6 and a 4 from C7R1.

Step 2 (Interactions & Turbos) …

· C4R1 & C4R3 create an Interaction with 5s, eliminating 5 as an option in C4R7 and C4R8.

· C9R1 & C9R2 form an Interaction with 4s, eliminating 4 as an option in C7R1, C8R1 & C8R2.

· C1R8 & C2R8 form an Interaction with 4s, eliminating 4 from C1R7.

Step 3 (Gordonian) … C7R4, C7R7, C8R4 & C8R7 form a One-Sided Gordonian Rectangle, eliminating a 7 from C8R6.

Step 4 (XY & XYZ – Wings) … C1R5, C9R5 & C7R6 form an XY-Wing, eliminating an 8 as an option from cell C8R5. (C9R5 is the “driver cell”. If C9R5 = 2, then C1R5 = 8, and C8R5 is not an 8. If C9R5 = 9, then C7R6 = 8 and C8R5 is not an 8. So regardless if C9R5 is a 2 or 9, C8R5 is not an 8, and therefore the 8 can be eliminated as an option from C8R5). From this point the puzzle is easily solved.

Puzzle # 9 Completed

In previous 2016 issues of TI LIFE Step 6, DAN’S YES-NO CHALLENGE was used to solve puzzles #2, 4, 6 & 8. It is a fun technique and I would strongly suggest reading the 16 pages devoted to this technique in my book. It explains in detail how to detect this Technique when working on your Sudoku puzzles.

As mentioned earlier you may use this technique to finish Puzzle #10, once you have exhausted Steps 1-5. See if you can find four Step 6 techniques that will break the puzzle!

Puzzle # 10

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

Again, if your puzzle does not look like the one above, you probably missed something in Puzzle Preparation. If so, and you do not find the clue, then I suggest you continue with the above to see if you can reach a conclusion to Puzzle #10.

Steps to complete Puzzle #10:

Step 4 (XY & XYZ – Wings) … C7R7, C7R8 & C9R7 form an XYZ-Wing, eliminating a 2 as an option from C7R8.

Step 6 (Dan’s Yes-No Challenge) …

· Consider cells C4R5 & C5R4, both having options 2 and 8; if C6R4 =2, then C3R4 is not a 2. If C4R5 = 2, then C4R8 is not a 2, then C5R9 = 2, then C1R9, C2R9 & C3R9 are not a 2, then either C3R7 or C3R8 = 2. Therefore, C3R4 again cannot be a 2. Therefore, C3R4 is not a 2 and can be eliminated as an option from that cell. Now use that same strategy for 8’s and you see that C3R4 cannot be an 8 either. Therefore, C3R4 = 6.

· In Step 6 above, we now have two unsolved cells in box 4, with “28” as options. If C2R6 =2, then C2R1 is not a 2. If C3R5 = 2, then C4R5 is not a 2, then C6R4 = 2, then C6R1 and C6R2 cannot be a 2, then C5R1 = 2, then C2R1 cannot be a 2. Therefore, the 2 can be eliminated as an option from C2R1. Now apply the same logic with 8s and you’ll see that C2R1 cannot be an 8, and therefore C2R1 = 1. The puzzle is easily solved at this point.

If you have any questions, comments, or suggestions to improve my monthly articles, I would really like to hear from you. You can post on this TI Life issue, or contact me directly at djlsuniverse@yahoo.com.

May the gentle winds of Sudoku be at your back!

By Dan LeKander, Wellesley Island, NY

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 three locations online, (djlsuniverse.com, amazon.com and ebay.com). Purchase of a book includes a 50-page blank grid pad, 33 black and two green tokens, to assist with Step 6.…

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.]