Can you believe how quickly summer left us at the River? Good thing we have Sudoku to keep our minds sharp through the off-season.
We start with a Sudoku puzzle in progress, where it appears that there are no more obvious or not-so-obvious clues. Can you find the hidden clue in Puzzle #122?
(The answer follows the conclusion of Puzzle #124, the feature puzzle for October)
Difficult rating … 4/10
(Rating based on puzzles not requiring advanced techniques)
Puzzle #123 should present a moderate challenge!
Difficult rating … 4/10
(Rating based on puzzles requiring advanced techniques)
Prior to utilizing techniques 1-8, complete the 5 Steps of Puzzle Preparation …
1. FILL IN DATA FROM OBSERVATIONS
2. FILL IN OBVIOUS ANSWERS
3. FILL IN NOT-SO-OBVIOUS ANSWERS
4. MARK UNSOLVED CELLS WITH OPTIONS THAT CANNOT EXIST IN THOSE CELLS
5. FILL IN THE OPTIONS FOR THE UNSOLVED CELLS
The first thing we observe is that C9R9=8 & C8R7=9.
In box two, a 7 can only exist as an option in C5R2 & C5R3; therefore, a 7 cannot exist as an option in C5R5 & C5R6.
Now your grid should look like Example #124.1 below:
This completes Puzzle Preparation Steps 1-4. Next, we will fill in options for all unsolved cells, giving us Example #124.2 below:
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 7. Steps 1-5 are relatively common techniques and are explained in the TI LIFE articles. Steps 6-Posts8 are covered in detail, in Dan’s book.
There are no Step-1-5 techniques hat can be further applied. Are there are any good Step 6 potentials. As in previous articles, we determined a particular number was a potential for a successful Step 6 exercise if that number appears as a given answer in 3 separate boxes, such that the boxes are not side-by-side, nor over each other. Which numbers do you see that are good candidates? Yes, the 5’s & 6’s.
We will start with the 5’s and perform a Step 6 exercise, Dan’s Yes-No Challenge”, per Example #124.3 below, using C3R1 & C9R1 as our starter cells highlighted in yellow.
Either C3R1 or C9R1 has to be a 5. First, we will assume C3R1=5 and mark it with a capital Y, for yes. Then we will mark the cells it affects with a Y or N, indicating a yes or no.
Next, we will assume C9R1=5, and mark it with a “y”. Then we will mark the cells it affects with a y or n.
We see that C5R6, C4R8 & C9R4 are marked N,n. It means that those cells cannot be a 5, regardless of which starter cell is a 5. The 5 can be eliminated as an option for those cells.
We also note that C4R4 is marked Y,y, which means this cell is a 5 regardless of which starter cell is a 5. So, C4R4=5
From this discovery, you are “off to the races”, and the puzzle leads to an easy conclusion, as per Example #124.4 below:
May the gentle winds of Sudoku be at your back.
By Dan LeKander, Wellesley Island
Thought of the day … a friend recently asked me regarding Sudoku, “have you always been good with numbers?” My reply was “yes, and I have always been good with letters, since you can perform Sudoku with letters A-I instead of numbers 1-9”. Of course, being proficient with Sudoku does not require any magical mastery of numbers or letters. It is purely a game of logic.
Clue for Puzzle #122 … did you find the clue? If not, read on.
Check row 6. What do you see?
We see that C1R6 & C8R6 have options 5 & 6. That leaves C8R6=9.
You may want to continue and see if you can solve the puzzle!