As the river warms heading towards summer, let’s keep our mind sharp with Sudoku!
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.
Difficult rating … 2 /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 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.
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
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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: