Chapter 28. Sudoku Example

Procedure 28.1. Task

1. Open sudoku.drl in the IDE.
2. Execute java org.drools.examples.DroolsExamplesApp and click on SudokuExample. The window contains an empty grid, but the program comes with a number of grids stored internally which can be loaded and solved.
3. Click on File Samples Simple to load one of the examples. All buttons are disabled until a grid is loaded. Loading the Simple example fills the grid according to the puzzle's initial state.
4. Click on the Solve button and the JBoss Rules engine will fill out the remaining values. The buttons will be inactive again.
5. Alternatively, click on the Step button to see the next digit found by the rule set. The Console window will display detailed information about the rules which are executing to solve the step in a readable format like the example below:

   single 8 at [0,1]
   column elimination due to [1,2]: remove 9 from [4,2]
   hidden single 9 at [1,2]
   row elimination due to [2,8]: remove 7 from [2,4]
   remove 6 from [3,8] due to naked pair at [3,2] and [3,7]
   hidden pair in row at [4,6] and [4,4]
   

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6. Click on the Dump button to see the state of the grid. The cells show either the established value or the remaining possible candidates. See the example below:

   Col: 0     Col: 1     Col: 2     Col: 3     Col: 4     Col: 5     Col: 6     Col: 7     Col: 8     
   Row 0:   2 4  7 9   2 456        4567 9   23 56  9  --- 5 ---  --- 1 ---    3  67 9  --- 8 ---     4 67   
   Row 1:  12    7 9  --- 8 ---  1    67 9   23  6  9  --- 4 ---   23  67    1 3  67 9    3  67 9  --- 5 --- 
   Row 2:  1  4  7 9  1  456     --- 3 ---      56 89      5 78       5678   --- 2 ---     4 67 9  1  4 67   
   Row 3:  1234       12345      1  45      12  5  8   --- 6 ---   2  5 78       5 78      45 7    --- 9 --- 
   Row 4:  --- 6 ---  --- 7 ---      5      --- 4 ---   2  5  8   --- 9 ---      5  8   --- 1 ---  --- 3 --- 
   Row 5:  --- 8 ---  12 45      1  45   9  12  5      --- 3 ---   2  5 7        567       4567     2 4 67   
   Row 6:  1 3   7    1 3  6     --- 2 ---    3 56 8       5  8     3 56 8   --- 4 ---    3 567 9  1    678  
   Row 7:  --- 5 ---  1 34 6     1  4 678     3  6 8   --- 9 ---    34 6 8   1 3  678   --- 2 ---  1    678  
   Row 8:    34       --- 9 ---     4 6 8   --- 7 ---  --- 1 ---   23456 8     3 56 8     3 56          6 8
   

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Procedure 28.2. Task

1. Open sudoku.drl in your IDE.
2. Click on File Samples !DELIBERATLEY BROKEN!. The JBoss Rules engine will inspect the grid and produce the following output:

   cell [0,8]: 5 has a duplicate in row 0
   cell [0,0]: 5 has a duplicate in row 0
   cell [6,0]: 8 has a duplicate in col 0
   cell [4,0]: 8 has a duplicate in col 0
   Validation complete.
   

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3. Click on the Solve button to apply the solving rules to this invalid grid. These rules use the values of the cells for problem solving. The rules detecting these situations insert a Setting fact including the solution value for the specified cell. This fact removes the incorrect value from all cells in the group.