ANN Sukodu puzzles--again

[Jim Hurley]

Our local paper has begun to carry a daily Sukodu puzzle. A friend 
challenged me to solve one that he had trouble with. I couldn't find 
a solution; I kept running into situations where I could find no 
possible entry without guessing.

To work on it I loaded up Alex Tweedly wonderful Sukodu Assistant. 
But I  needed something that would determine in there was a unique 
one-stage solution, i.e. a solution in which there was always at 
least one cell  with a determined digit, given the present 
configuration.

Well, one thing lead to another and Sukodu--see below--resulted. It 
uses Alex's very nice interface. The drop down menu is an excellent 
way to enter this limited assortment of discrete data into a field.

The stack also does an analysis of the puzzle after each step and 
will display in each cell the possible entries. It also looks at the 
constraints on rows, columns, and blocks, to determine what's 
possible in these components--applying the restriction that each row, 
column and block are to contain all nine digits. This analysis is 
displayed in separate fields.

If you choose the mode in which this info is displayed, the solution 
to any puzzle will be trivial. But I found it a very useful tutorial 
to run through a few of the harder puzzles this way. There were 
strategies available which I had never guessed at. (You can toggle 
the display of this analysis on and off with a right-click or 
control-click. You can turn any  entry green with a shift-click. This 
is useful if you have to make a guess. Then, if  you run into a 
contradiction at some point down the road, you can undo back to the 
green entry.)

When the puzzle is first loaded, the stack uses this analysis of 
rows, columns and blocks to run through the puzzle (with the screen 
locked) step by step to obtain a solution--if there is a one-stage 
solution. With this solution available, it is then possible to choose 
a mode of play which will not allow an incorrect entry into a 
cell--comforting.

I have tested this in Mac OS X, but not thoroughly in Windows. I had 
one stinker of a problem with the Window version. It read a menuPick 
handler in a button which I had commented out, and did not pass the 
menuPick message to the card. Took a while to find this bug.

Turned out that the puzzle my friend had given me was missing a 
number. With friends like this----

The stack (and file folder) are at:

  http://home.infostations.net/jhurley/SudokuFolder.zip

Keep the file folder with the stack. The folder contains a few 
additional puzzles and a place to save your own.

I may never do one of these Sudoku puzzles again.

Jim