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Sudoku Puzzle Challenge–March 2016


Are you ready for another Sudoku challenge this month?

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

DAN’S 8-STEP APPROACH TO SOLVING 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 …

2015/16 TI LIFE SUDOKU ARTICLES

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

Sept 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

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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

This eight step approach will solve virtually all published Sudoku puzzles. In my experiences in solving over 1500 puzzles, this approach has yet to fail.

PUZZLE #3 that follows is nothing but pure fun. It can be solved with Steps 1-5. SUGGESTION: Master Steps 1-5! About 75% (or more) of all published Sudoku puzzles can be solved with good Puzzle Preparation and steps 1-5. And please remember to search for obvious pairs in the Puzzle Preparation phase to save you lots of time.

March 16 example 1

PUZZLE #3

 

You may want to print this entire article to do the puzzles and have a “portable” guide to the solution if needed.

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

Puzzle 3 through preparation

PUZZLE #, with PUZZLE PREPARATION

 

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 #3:

1. Cells C4R3 (column 4, row 3) & C6R3 are the only two cells in box 2 that have a 1 and 4 as options (Pair), so you can eliminate the options 2 & 6 from cell C6R3.

2. This newly marked pair eliminates the 1 as an option from cells C1R3 & C3R3.

3. C1R2 & C3R1 form a Turbo and the 3 can be eliminated as an option from C6R7.

4. C5R1 & C5R3 create an Interaction such that the 2 can be eliminated as an option from C5R8.

5. C2R8, C3R8 & C5R8 form a Triplet in row 8. The 1, 6 & 9 can be eliminated as an option from all other cells in row 8. That leaves C8R8 with only an 8 as an option. Mark that cell an 8. Then C8R5=6. C9R5=8. C8R9=1.

6. C2R4 & C2R9 form a Pair (36), so eliminate the 6 as an option in C2R8.

7. C4R7, C6R7 & C9R7 form an obvious Triplet in row 7, and the 1, 5 & 6 can be eliminated from C3R7 & C5R7.

8. C2R9, C3R3 & C3R7 form an XY-Wing, with cell C3R7 being the “driver” cell. If C3R7=3, then C2R9= 6. If C3R7=9, then C3R3=6. So regardless of whether C3R7 is a 3 or 9, C3R8 cannot be a 6, so you can eliminate the 6 from C3R8 as an option.

9. This leaves C2R8 & C3R8 both having the options 19, then C5R8=6, C3R7=3, C2R9=6, and the puzzle is easily solved from here.

Again, Master Steps 1-5! Can you imagine how hard the puzzle would be if you missed any of these Step 1-5 clues? The answer to the puzzle follows:

Puzzle 3 completed

PUZZLE #3 COMPLETE

 

In the February 2016 issue of TI LIFE, Step 6 was introduced to you, entitled DAN’S YES-NO CHALLENGE. It is a rather 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. To keep the momentum moving forward, Puzzle #4 requires you to complete Steps 1-5 and then move on to Step 6. See if you can find two Step 6 situations that will break the puzzle!

Puzzle 4

PUZZLE #4

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

Puzzle 4 through completion

PUZZLE 4 with PUZZLE PREPARATION

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 #4.

Unless I missed a clue, there are no Step 1-5 clues, so we move directly to step 6.

1. C4R1 & C6R3 are the only two cells in box 2, with a 6 as an option, and therefore one of those two cells must be a 6. Again, when I name a cell Yes, it means we are calling it a 3. Likewise, when I name a cell No, it means it cannot be a 6. First we will assume C4R1 is Yes. Then C4R8 is No. If C5R3 is Yes, then C7R3 is No, then C8R1 is Yes, then C8R9 is No, then C9R8 is Yes, and then C4R8 is No. So regardless of which of the two cells in box 2 is a 6, C4R8 is not a 6 and the 6 can be eliminated as an option for that cell.

2. C7R3 & C8R1 are the only two cells in box 3 with a 6 as an option, and therefore one of those two cells must be a 6. First assume C7R3 is a Yes. Then C5R3 is No, then C4R1 is Yes, and then C4R5 is No. Next assume C8R1 is Yes. Then C8R9 is No, then C9R8 is Yes, then C5R8 & C5R6 are No, then C4R7 is Yes, then C4R5 is No. So, regardless of which cell in box 3 is a 6, C4R5 cannot be a 6, leaving 1 as the answer to that cell. The puzzle is easily solved from here.

Your puzzle should look like this when complete:

Puzzle 4 completed

PUZZLE #4 COMPLETE

Well, I hope you have enjoyed the two Sudoku puzzles this month. See you in April.

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.]

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