Creating an Extreme Sudoku Puzzle from Scratch

In this tutorial you will see how to create an extreme Sudoku puzzle for scratch.  This is a four step process.  We will be using Hodoku throughout this tutorial.  The reason is Hodoku’s cell coloring features will allow us to keep track of what we have done and then indicate to us what we need to do next.  This is not simple process.  If you plan to attempt to create puzzles this way you will need a little practice before you get good at it.

Step 1 – Create a Values Grid

We start with the following seed puzzle or Solution Grid:

Next, we launch Hodoku and put it in receive new givens entry mode:

We take the values and givens in our Solution Grid and set the value in each cell:

We save our Values Grid to a local file:

We use the file name “p1 Values Grid” and click on the “Save” button:

This completes Step 1.

Step 2 – Create an Initial Starting Point:

Next, we create the initial starting point of our creation process.  This is done by picking 1 to 3 blocks and creating a symmetrical or asymmetrical pattern.  From the Values Grid we created in Step 1 we create our initial starting point:

In the next step, we will leave blocks 4, 5, and 6 intact.  Before we continue, we first save our initial starting point:

We use the file name “p1 Starting Point” and click on the “Save” button to continue:

Before we can continue to the next step, we must first confirm we have a valid starting point puzzle.  From Hodoku’s “Edit” drop-down menu we select the “Copy Values” command:

We launch a new copy of the Hodoku program and from the new Hodoku drop-down “Edit” menu we select the “Paste” command:

If our puzzle is still valid, we will see a set of puzzle solving techniques in Hodoku’s Summary windows:

And at the bottom of Hodoku we would see a difficulty score:

If our puzzle were not valid, we would see the dreaded multiple solutions dialog box:

But our starting point is valid so we can continue to Step 3. 

This completes Step 2.

Step 3 – Create a Symmetry Grid:

Next, we are going to do a series or sequence of symmetrical deletions from our starting point.  If we delete a start point grid value from block 1, we then also delete the same symmetrical location in block 9.  Each time we check if we still have a valid puzzle.  If we do not have a valid puzzle we back out of the changes.  After we are done, we save the Symmetry Grid to a file named “p1 Symmetry Grid”.

Here is the result:

When we deleted from block 1, we deleted from block 9.  When we deleted from block 2, we deleted from block 8.  When we deleted from block 3, we deleted from block 7.  We did not delete anything from block 4 but if we had we would have deleted from block 6.   As stated, for this step we were keeping blocks 4, 5, and 6 intact as our initial asymmetrical starting point.

This completes Step 3.

Step 4 – Asymmetrical Deletions:

To find an extreme puzzle we are going to take our Symmetrical Grid and start deleting values one at a time.  To be consistent and keep track of what we are doing we do the sequence of deletions according to an algorithm.  For this example, here is the asymmetrical deletion algorithm:

This algorithm has two paths.  Once we have a successful deletion, we will switch to the other path.  Here is the initial starting point of the deletion algorithm:

Cell R5C7 is the first cell we will delete and test to see if we still have a valid puzzle.  If we do still have a valid puzzle, we will color the location purple to indicate it was one of the original Symmetrical Grid locations.  We will then keep track of our Summary window list and Hodoku difficulty score as we progress.

When we delete the value at cell R5C7 here is the result:

We color the cell background of R5C7 in purple to indicate it was a location for a Symmetry Grid value.   Here is the resulting Summary window:

Here is the resulting score:

Cell R8C9 is the next value to delete according to our algorithm:

We succeed in deleting cell R8C9.   We now have a difficulty score of 334.  We switch back to the first path and continue this process.  Here is the next meaningful result. 

When we delete the value at cell R2C4 we get the following summary:

We now have a difficulty score of 438.  We continue the process. 

When we delete the cell at R1C8 we find our first extreme puzzle:

We color the background of cell R1C8 the color peach to indicate we have found a piece of fruit.  We now have an extreme puzzle having a difficulty score of 2212.  We could stop here but we continue looking for more pieces of fruit. 

Here is our final result:

And here is the final summary result:

We have created an extreme puzzle with a WHOPPING score of 12990!

Related Videos:

dxSudoku #58 Part I Creating Puzzles from Scratch – Seed Puzzles
dxSudoku #59 Part II Creating Puzzles from Scratch – Puzzle Creation
dxSudoku #60 Part III Creating Puzzles from Scratch – Special Topics