Forrest Gump might say, “Sudoku is like a box of chocolates; you never know what you’re going to get”.
Please enjoy the puzzles for this month.
Please let the author and this editor know how you managed.
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 #137?
(The answer follows the conclusion of Puzzle #140, the feature puzzle for this month)
Difficult rating … 7/10
(Rating based on puzzles not requiring advanced techniques)
Impossible to solve?
Impossible? No. Difficult? Extremely.
Puzzle #139 should be challenge for you. Advanced Techniques (Steps 6 and/or 7) are required. Difficult rating 9.8/10.
Difficult rating … 3/10
(Rating based on puzzles requiring advanced techniques)
Prior to utilizing techniques 1-8, complete the 5 Steps of Puzzle Preparation …
- FILL IN DATA FROM OBSERVATIONS
- 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
The first thing we observe is that C4R7=7. C8R5=8. C6R8=9. C5R7, C5R8 & C5R9 are limited to options 1, 4 & 8. This leaves C5R1, C5R3, C5R4 & C5R5 with options 2, 3, 5 & 6.
In box six a 4 can only exist as an option in C8R6 and C9R6; therefore, a 4 cannot exist as an op-tion in C1R6, C3R6, C4R6 and C6R6.
In box six a 7 can only exist as an option in C7R4 and C7R5; therefore, a 7 cannot exist as an op-tion in C7R1 and C7R3.
In column two the options 2 and 3 can only exist as options in C2R5 and C2R7.
Now your grid should look like Example #140.1 below:
This completes Puzzle Preparation Steps 1-4. Normally, next we would fill in options for all of the unsolved cells. However, there are two options that would make excellent candidates for Step 6 exercises.
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 2’s & 3’s. We do not need the options of the unsolved cells to be listed in order to con-duct these exercises.
If one or both of these exercises is successful, we could save quite a bit of time not having to fill in the options for all unsolved cells and potentially shortening the time to solve the puzzle.
We will start with the 2’s and perform a Step 6 exercise, Dan’s Yes-No Challenge”, per Example #140.2 below, using C2R5 & C2R7 as our starter cells highlighted in yellow.
Either C2R5 or C2R7 has to be a 2. First, we will assume C2R5=2 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 C8R7 & C3R8 are marked N,n. It means that these cells cannot be a 2, regardless of which starter cell is a 2. The 2 can be eliminated as an option for those cells.
Now, in Example #140.3 below we will conduct the same exercise with the 3’s with the same starting cells.
We see that C7R3 & C9R7 are marked N,n. It means that these cells cannot be a 3, regardless of which starter cell is a 3. The 3 can be eliminated as an option for those cells. We also see that C7R8 is marked with a Y,y, meaning that cell is a 3 regardless of which starting cell is a 3; there-fore, C7R8=3.
Now our grid should look like Example #140.4 below:
In box nine a 2 can now only exist as an option in C8R7 and C8R8; therefore, a 2 cannot exist as an option in C8R1, C8R2 and C8R3.
This leaves C7R1 as the only unsolved cell in box three that can be a 2. C7R1=2. Then, C6R2=2. C5R5=2. C3R6=2. C2R7=2. C8R8=2. C3R7=3. C2R5=3. C4R6=3. C5R3=3. C9R2=3. C6R3=6. C8R2=6, and so forth, leading us to an easy conclusion, as per Example # 140.5 below.
This feature puzzle is an example of being solved by just two Step 6 exercise, and we did not even have to fill in the options for the unsolved cells. This clearly illustrates the power of a successful Step 6.
May the gentle winds of Sudoku be at your back.
By Dan LeKander
Clue for Puzzle #137 … did you find the clue? If not, read on.
Check row 3. What do you see?
We see that C6R3 & C7R3 are the only two cells in row 3 that can have options 4 & 9. Now, the only unsolved cell in row 3 that can be a 5 is C5R3. C5R3=5. This puzzle will be interesting to complete, requiring advanced techniques. Difficult rating = 7/10.
Editor's Note: Hard to believe we are into 2023 and that our friend Dan LeKander has provided 4 more puzzles. Looks like he will do so in the coming months, so your challenge Sudokus are alive and well.
Recently someone wrote to ask how to fill them out online. Unfortunately, you need to print them yourself, but that is easy to do and I know you will have just as much fun.
And, if you have not already done so, I suggest you purchase Dan’s book: