As the river warms heading towards summer, let’s keep our mind sharp with Sudoku!
Clueless?
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 #145?
(The answer follows the conclusion of Puzzle #148, the feature puzzle for this month)
Simply a Logic Puzzle
Difficult rating … 3/10
(Rating based on puzzles not requiring advanced techniques)
Impossible to solve?
Impossible? No. Difficult? Extremely. Puzzle #147 should be challenge for you. Advanced Techniques (Steps 6 and/or 7) are required. Difficult rating 9.5/10.
Feature Puzzle
Difficult rating … 2 /10
(Rating based on puzzles requiring advanced techniques)
PUZZLE PREPARATION
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 C2R9=1 and C3R7=3. Now, C1R7, C1R8 & C1R9 have options 6, 7 & 8.
In column 4, C4R3 & C4R9 are the only two cells that can have options 5 & 9.
In box 3 only C7R2 & C8R2 can have a 6 as option; therefore, C2R2 & C3R2 cannot have a 6 as an option. Indicate this by placing a small 6 in the bottom of those two cells.
In box 5 only C5R5 & C6R5 can have a 7 as an option; therefore, C2R5 & C3R5 cannot have a 7 as an option.
Now your grid should look like Example #148.1 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 5’s & 9’s. We do not need to show the options of the unsolved to conduct 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 first perform the Step 6 exercise with the 5’s per example #148.2 below, using C3R5 & C7R5 as our starter cells highlighted in yellow.
We see that C3R3 & C6R2 have N,n designations. This means those two cells cannot be a 5 regardless of which starter cell is the 5. We can remove the 5 as an options from those cells. For our illustration, we will place a small 5 at the bottom of those two cells.
We will perform the Step 6 exercise with the 9’s per Example #148.3 below, using C2R5 & C8R5 as our starter cells highlighted in yellow.
Either C2R5 or C8R5 has to be a 9. First, we will assume C2R5=9 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 C8R5=9, and mark it with a “y”. Then we will mark the cells it affects with a y or n.
We see that C2R3, C5R2 & C4R9 are marked N,n. It means that these cells cannot be a 9, regardless of which starter cell is a 9. The 9 can be eliminated as an option for those cells.
We also see that C4R3 is marked Y,y, which means C4R3 is a 9 regardless of which starter cell is a 9; therefore, C4R3=9.
Now our grid should look like Example #148.4 below:
You can easily see that C6R3=5, C4R9=5, and so forth. The 5’s are easily solved, and then the 9’s, leading to an easy solution per Example #148.5 below.
This puzzle reflects the power of Step 6 to reduce a difficult puzzle to an easy solution.
May the gentle winds of Sudoku be at your back.
Dan LeKander
Clue for Puzzle #145 … did you find the clue? If not, read on.
Check Column 9. What do you see?
C9R3 C9R6, C9R7, C9R8 & C9R9 are limited to options 1, 2, 3, 4 & 5. C9R9 has given answers 1, 3, 4 & 5 either in row 9 or Box 9; therefore, C9R9 can only be a 2. C9R9=2.
Important Editor's Note
We need to hear from you - do you work on Dan's Sudoku's Puzzles?
Dan would like to hear more from his readers, such as questions, comments & suggestions - info@thousandislandslife.com. We will forward this to Dan, and he will contact you directly. Thank you."
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. Also you can use a grid sheet and copy numbers onto the grid.
And, if you have not already done so, I suggest you purchase Dan’s book: