Susie asked for an easier puzzle, so this month we will please her. There are no advanced techniques, Steps 6-8, required, but you will need to play your “A” game to solve. [Editor's Note... Thanks Dan!]
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 techniques first complete the 5 Steps of Puzzle Preparation …
- FILL IN DATA FROM OBSERVATIONS, such as obvious pairs or triplets
- 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.
We will start with the 1’s and navigate through 2’s to 9’s, then repeat the process until we conclude all Puzzle Preparation Step 1-4 clues.
The first thing we observe is that C2R3 (cell in column 2, row 3) =7(obvious answer). Then, C1R8=7. C9R2=7. C8R6=7. C6R5=7. C4R7=7. That retires the 7’s. C3R6=8. C7R5=5. C1R6=5. C1R4=1. C9R6=1.
In box 5 the only cells that could have a 2 as an option are C4R4 or C6R4; therefore, a 2 cannot exist as an option in C7R4-6. Therefore, C9R5=2.
In box 3 the only cells that can have a 3 as an option are C8R1 or C9R1; therefore, a 3 cannot exist an option in C1R1, C2R1 or C3R1. Therefore, C3R2=3.
In column 1 a 2 cannot exist as an option in C1R5 or C1R9; therefore, C1R1=2. The options for C7R4, C8R4 and C9R4 are limited to 469, an obvious triplet. The options for C7R8 & C9R8 are 68, an obvious pair. The options for C4R9 & C6R9 are 68, an obvious pair. The options for C4R6, C5R6 & C6R6 are 469.
The options for C4R4, C6R4 and C5R5 are limited to 238. There is already a 28 in row 5; therefore, C5R5=3. C4R8=3. The options for C4R4 & C6R4 are now 28
C2R4=3.
The options for C1R5, C2R5 & C3R5 are limited to 469. There is already a 4 and 6 in column 1; therefore, C1R5=9. C1R9=3. The options for C2R5 & C3R5 are 46.
In box 2 a 5 must exist in C4R1-3; therefore, a 5 cannot exist as an option in C6R1 or C6R2. Given that, the only cell in row 2 that can be a 5 is C4R2. C4R2=5.
That wraps up Puzzle Preparation steps 1-4, so now your grid should look like Example #71.1 below:
That wraps up Puzzle Preparation steps 1-4, so it is time to complete step 5 by filling in the options for the remaining unsolved cells. Now your grid should look like Example #71.2 below:
TECHNIQUES STEPS 1-5
In column 5 the three cells C5R2,7,8 have options 149, an obvious triplet; therefore, the other unsolved cells in column 5 cannot have options 149. Then, C5R6=6 and C5R3=8. C9R3=9.
Now, either C5R2 or C6R2 must be a 9; therefore, you can remove the 9 as an option for C4R1 & C6R1.
Now your grid should look like Example #71.3 below:
At this point we have created an obvious triplet. Can you spot it?
In column 4 we have three cells that share 3 options … C4R3, C4R4 & C4R9 share options 268, so we can remove those options from the other unsolved cells in column 4. C4R1=4. C4R6=9, and so forth, leading to an easy solution per Example #71.4 below:
We all learned from this puzzle how important it is to revisit common techniques after we have made changes to a puzzle. Hope you have enjoyed this puzzle.
May the gentle winds of Sudoku be at your back.
Dan LeKander
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Editor's Note: Again, I want to thank Dan…and his proofreader… Peggy! I wrote last month that this editor can find 1001 reasons to do something other than dusting... so I know how hard it is to actually buckle down and not go fishing unless you have closed up and headed to the winter digs... So thank you Mr. and Mrs. LeKander - we have come a long from from 2016!
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: