Homework 11: Sudoku Solver
Milestone 1 Due: Mon. 18 April 2011 at 9:59:59 am
Milestone 2 Due: Friday 16 22 April 2010 2011 at 9:59:59 am
...
am
Tip: Out of Memory Error
Try the following: Go to Edit/Preferences/Micellaneous/JVMs
and add the -Xss64M
option to the "JVM Args for Interactions JVM
" line to increase th amount of memory used.
The Sudoku Game
Sudoku is a 9*9 9x9 grid-based puzzle in which the goal is to place numbers from 1 to 9 in the grid squares taking into account specific constraints. The 9 * 9 x 9 puzzle grid can be seen as divided into 9 sub-grids of size 3*33x3. The 3 main conditions in the classic version of Sudoku state are that each square in the grid contains a number from 1 to 9 and a number cannot be repeated:
- In any line
- In any column
- In any on the 3*3 3x3 sub-puzzles
Sudoku is not limited to 9x9 boards. An "order" for a Sudoku puzzle can be defined, and thus a Sudoku puzzle is an order
2
x order
2
matrix. A regular Sudoku puzzle is this order = 3
. The above rules can be generalized to any order. This is Rice, so our system should be able to handle any order of Sudoku puzzle.
For more information of the game of Sudoku, visit: http://en.wikipedia.org/wiki/Sudoku
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A Sudoku puzzle as needed for this assignment may not be well formed and in general may have no solutions or multiple solutions. Your solution must be able to handle these situations! (You only have to find one solution, if one exists however, not all solutions.)
Supporting Code Download
The support code provided contains a DrJava project, some sample puzzle boards and a simple Junit test.
Download the code here: HW11.zip
Full Javadocs are available in the supplied code in the docs
folder. Simply open the index.html
file in your browser.
The assignment
The purpose of this assignment is to build a Java solver that finds all one of the different any possible solutions of the game using a constraint-based approach.
...
- An empty board is fully determined by a single value, it's "
order
", which for a 9x9 board is 3. - The board is viewable in terms of rows, columns and blocks.
- Each row, column and block has exactly
order*order
2
cells, e.g. fororder
= 3, each row, column and block has 9 cells. - Each board has exactly
order*order
rows2
rows, columns and blocks.
- Each row, column and block has exactly
- Each cell is a member of exactly one row, one column and one block.
- No rows share the same cell. Likewise, no columns or blocks share cells. This forces the square matrix layout of rows, columns, and
orderxorder
order
^2
sub-matrix of blocks if one were to display the rows, columns and blocks where each cell is only shown once.
- No rows share the same cell. Likewise, no columns or blocks share cells. This forces the square matrix layout of rows, columns, and
- The rules of Sudoku stipluate that the value in any given cell has very specific constraints:
- unmigrated-wiki-markup
- The valid values are {{
1...order
*order}}2
(inclusive), e.g. for order=2, the allowed values are \ [1, 2, 3, 4\] - Any valid value in a cell cannot appear in another cell in the row, column or block to which that cell belongs. Conversely, each row, column or block must contain every valid value exactly once.
- The valid values are {{
...
What does this all mean? ==> Rows, columns and blocks can all be represented with the same data structure! We will use the interface ICellSet
to represent the set of cells corresponding to a particular row, column or block. There is also the implication that each cell "knows" which specific row, column and block to which it belongs, so each ICell
has a set (vector) of ICellSets
that correspond to the row, column and block to which that cell belongs (in that order).
A "board" is therefore a set of three Vector<ICellSet>s
representing the rows, columns and blocks of the board. Note that any given cell will appear once in the rows, once in the columns and once in the blocks. The data structures that we have created enable us to access the cells in multiple methods that clearly represent the cell relationships in the manner that best models the problem at hand, namely the Sudoku board. We can easily and consistently see the cells in terms of rows or columns or blocks in a manner that is abstractly equivalent, enabling us to easily reuse the same code to process the cells in any direction we choose. Compare this to a standard NxN matrix representation (In the support class, the Sudoku grid is modeled by an array of Rows. The Row class contains an ArrayList of HashSets, one HashSet of Integers for each square from that row. The HashSet contains possible values for the square.
To find final solutions from a partial solution, one should look for a square with multiple possible values, generate the different partial solutions by specifying that the square contains one of the values (and impose the restrictions specified by the rules of Sudoku on the content of the other squares), and then recurse for each of these possible solutions until no square has more than one possible value. If square becomes empty, then it will not lead to a final solution. If all squares have exactly one value, then we have a final solution.
The support code provided contains a DrJava project and a few simple Junit tests. The code download is coming "Real Soon Now" ...
Your assignment is to implement:
- the method findSolution in the PartialSolution class.
- at least 5 more tests (3 for findSolution, 1 for isDeadEnd, 1 for isFinal).
Extra credit
For extra credit, improve the implementation of setElement and/or findSolution as you see fit, in order to improve the performance of the algorithms by examining fewer PartialSolution's. The improvement will be quantified by seeing if there is a decrease in the count of partial solutions in order to solve a puzzle (the count of partial solutions is returned by the getIntermediateSolutions() function of the PartialSolution class ).
a collection of rows) which represents only a single cell relationship feature, namely that they are in rows. Luckily, accessing the cells in terms of columns is not too difficult, but accessing them in terms of blocks is a bear!
Solving Sudoku
The fundamental principle of Sudoku is that any given row, column or block must contain all integers from 1 to order*order
inclusive, exactly once.
In the beginning, a Sudoku board is defined by particular cells already being solved (i.e. have a single value in them) and all the rest being unsolved (i.e. have all possible values in them). We can think of an unsolved cell as containing all possible guesses for the value at that moment, which at the beginning, is all possible values.
Thus the simplest reduction process is to look at the set of all values from the solved cells in the row, column and block to which a cell belongs and eliminating those values from the current set of value choices for that cell. (Hint: HashSet<T>.removeAll()
does exactly what you want!) To reduce a cell set is to reduce every cell in that cell set. To reduce a board is to reduce every cell in any collection of cell sets -- do you need to reduce every collection of cell sets?
Requirement: the reduction process for a cell set and for a board should be able to detect if the cell set or board is
- Irreducible - the reduction pass did not change any values but at least one cell is unsolved.
- Solved - all the cells were solved already or became solved
- Unsolvable - a cell somewhere has or ends up having no value choices left, i.e. and empty
HashSet
of values. - Reducible - a change to the number of values for a cell somewhere occurred.
Irreducible Sudoku boards ARE potentially solvable
You must first get a simple reduction pass working! Do NOT attempt to solve irreducible boards until you are confident that your simple reductions are working properly!
But once your simple reduction operational, you can tackle how to deal with irreducible boards. An irreducible board means that a reduction pass on the board causes no change even though the board contains at least one cell that is neither solved nor empty. To solve an irreducible board, you need to pick a particular unsolved cell from the board using some sort of heuristic to choose what you think is the best cell to work with, and test each of its values one by one to see if they lead to a solved board. To test a value, pick on of the values, set the cell to have that one value, i.e. to be "solved" and then try to solve the entire board. If the board is solvable, you're done, otherwise, take the next value choice and repeat.
'But this trial process requires that you be able to return the board back to its original state before you tried the previous choice! Luckily, a Board
object is capable of making a "deep" copy (clone
) of itself which you can save away. Unluckily, the method to find a cell candidate (findMinChoiceCell
) only returns the cell, not its location in the puzzle, so you don't know which cell you actually found (does it matter?). See below for a tip on one way to get around this problem.
Note that the process of solving an irreducible board may itself encounter an irreducible board which you must then solve, so the overall solving process must fundamentally be a recursive process!
See the code details wiki page for explanations of the return types of the reduction and solving methods of GameModel
.
Supporting Code Details (click to go to next wiki page)
Running the Application
Starting the program:
Start the program by running the* Controller
class. The supplied DrJava project should already be set to run this class when you click "Run Project".The program will come up with an order 3 board with empty cells. You can change the order by changing the number in the "Game Order" text box and press the Enter
key.
*Entering values:*You can enter values into the cells by clicking on a cell and typing in a number and then either pressing the Enter
key or by clicking on a different cell.To enter multiple values in a cell, separate the values by spaces and/or commas. You can pre-load guesses this way.To enter all possible numbers into a cell, as the start of a game would require for cells that are not initially supplied, either enter all possible values or enter a dash, -. Remember that an empty cell means that the puzzle is not solvable! The start of a game should have some cells with single values and the rest with dashes.
Loading values from files:
Clicking the Load
button will open up a standard file dialog window where you can browse to and select a values file to load.A values file is a normal text file that can be created on any text editor and has the following format:
- Each line of text represents a single row of cells.
- Each cell's values are separated from the other cell's values by a space or tab (tab is recommended because it will keep your values nicely lined up and easy to read).
- Multiple values for a single cell are separated by commas with NO spaces.
- A dash means "all possible values" for the cell, e.g. for an order 2 board, "-" is a shortcut for "1,2,3,4"
- A zero in a cell means that the cell is empty
A standard valid puzzle starting file should therefore have only single values and dashes.
Test files may have empty cells (zero) or cells with specific value choices in them to test specific features of the program.
Available test data:
A number of test data files have been supplied but are in no way to be considered comprehensive or exhaustive!
Saving cell values from the program:
Clicking the save
button will bring up a standard file dialog window where you can browse to and save the current cell values as a text file.
The program does NOT warn you about overwriting existing files!!
The file format that the program saves is identical to the format used for loading, so cell values can be saved and re-loaded.
Validate the Board:
Clicking the Validate Button
button will pop up a message dialog box with information on the state of the board. This button, which is fully operational in the supplied code, is a very useful tool to check your code's performance as you work. The information shown includes
- If the board is solved.
- If the board is valid but not solved. The board could be irreducible however.
- The board is invalid
- The same value appears more than once -- the offending row, column or block is shown
- An invalid value is present, e.g. a negative number -- the offending row, column or block is shown.
- A cell is empty - Only one empty cell per cell set is detected. There may be more empty cells present.
All recution and solving operations should always leave the board in a valid state, unless the board is unsolvable, wherein a cell may become empty.
See the note about the GameModel.validateBoard()
method in the Code Details wiki page!!
Perform a Single Reduction Pass on the Board.
When your reduceBoard()
method is working, clicking the Reduce
button will perform a single pass reduction on every cell on the board. You should thus be able to progress towards a solution by repeatedly clicking the Reduce
button, though you might end up with either an unsolvable or irreducible board. Attempting to reduce an unsolvable or irreducible board will have no effect on the board.
Find a Minimum Choice Cell
When your findMinChoiceCell()
method is working, clicking the Find Min Choice Cell
button will pop up a message dialog box displaying the contents of the chosen cell. It does not show the location of the cell because that information is not available. Which cell is chosen depends on the heuristic used. One can manually attempt to solve an irreducible board by getting the values of the cell to be replaced and removing all values except one from the selected cell and then trying to further reduce the cell.
Solve the Board
Once your solve()
method is working, clicking the Solve
button will attempt to solve the board from its current configuration. The result will be a pop-up saying that the board is either solved or unsolvable.
During the middle of your implementation, after you have implemented the reduceBoard
but before you have implemented the solveIrreducibleBoard
method, you should do a partial implementation of solve that can solve an easy-level puzzle that never encounters an irreducible board. At that point, the Solve
button may return a message saying that the board is irreducible.
Generating Solvable Puzzles
A separate, stand-alone, fully-functional utility has been provided that can generate 9x9 Sudoku puzzles from a store of over 50,000 puzzles. The utility consists of a singleton utility class GeneratePuzzle
and a companion GUI application to run it, GeneratePuzzleApp}. The utilities utilize the files in the {{HW11\data\puzzle_src
folder.
- .In DrJava, right-click the
GeneratePuzzleApp
class and select "Run File" to start the utility. - Select a file from the drop-list (yes,
4,txt
is missing--broken link on the download page). The higher the number, the harder the puzzles. - Each file contains about 10,000 puzzles. Use the number spinner to choose or type a puzzle number from 1-10,000 (approx.). Specifying "0" as the index will cause the utility to randomly select a puzzle.
- Click the
Generate
button and the puzzle will appear in the main display area of the utility. - Click the
Save
button to save the generated puzzle in a format that the Sudoku solver application can now read.
This should keep you busy for a while, though your Sudoku solver should be able to easily solve any puzzle in the collection.
Note: Your Sudoku solver should be able to solve a completely blank puzzle (all dashes, not empty)!
Programming Tips
Updating the View
At the end of the reduceBoard
and solve
methods, be sure to add the line
Code Block |
---|
view.setCellViews(currentBoard.blks);
|
This will update the view with the mutated board. (Note that the IViewAdapter.setCellViews()
wants the cells in the format of the blocks, not the rows, because that's how the screen is laid out.)
Your board on the screen will NOT reflect the changes of your algorithms unless you add this line!!
Mutating a value outside of an anonymous inner class:
The quandry is that a variable that is declared outside of an anoymous inner class, e.g. visitor implementation, that is accessed by the anonymous inner class must be defined as final
(Thanks Sun! Argh...). There a classic "hack" to get around this:
Define your variable as a one-element array.
For instance:
Code Block |
---|
final int[] x = new int[]{0};
final ICell[] aCell = new ICell[]{ new Cell() }; |
An anonymous inner class can thus access these variables by using the array syntax: x[0]
and aCell[0]
You may find that in order to keep track of several properties as you loop through cells and cell sets, that you may need to create multiple one-element array values.
Controlling a loop from inside of an anonymous inner class
Unfortunately, you cannot break
or continue
a loop while inside of an anonymous inner class that the loop completely encloses (i.e. the anonymous inner class is defined in the body of the loop). There are two ways to accomplish this though:
- Return a
boolean
or other primitive value from the anonymous inner class (which is probably a visitor being accepted). Based on the returned value, break or continue with the loop. Note that returning a value to which you delegate to, e.g.IUtilHostAB/C/D
, will not work because you will just find yourself inside another anonymous inner class. - Use the one-element array trick described above. Set its value from inside the anonymous inner class. After the anonymous inner class returns, break or continue the loop based on that value.
How to make copies of a board when you don't know which cell is the one you want to guess from
The problem is that if you lose the reference to the cell that you chose to test its values, you can never find that cell again without doing the whole search over again. This is because a cell doesn't know where it is in the board (it never needs to know!).
The trick is to keep references to everything you need and to make copies at just the right time. So here's what to do:
- Keep references to BOTH the original board and the cell you found.
- Get an array copy of the values in the cell.
Cell.getValueArray()
makes a copy. You can use this array to loop over. - In your loop:
- Clear the contents of the cell. This will mutate your original board!
- Set the value of the cell to the desired test value.
- Make a copy of the orignal board.
- Solve the copy of the board -- you will need to set the current board to the copy. Don't mess up the original board!
- Repeat with the next test value if no solution or quit if you find a solution.
Requirements
Your assignment is to implement the following methods of GameModel
:
Milestone 1
reduceCellSet
(15 pts)reduceBoard
(15 pts)solve
-- partical solution for easy puzzles that have no irredicible states.
Milestone 2
findMinChoiceCell
(15 pts) -- Be sure to describe what your heuristic is trying to do in some comments accompanying your code! Simply picking the first or a random cell will NOT garner full credit!solveIrreducibleBoard
(20 pts)solve
- full solution (20 pts)
You are also required to have complete unit tests for the above methods. (15 pts)
Javadocs are already complete in the supplied code. If you add any fields, methods or classes, complete Javadocs will be expected for them. It is suggested that you do some level of Javadocs for your anonymous inner classes, if only to help keep things straight in your own head.
Your code must work for ANY order puzzle! (To within machine limits, of course.)
Testing Procedures
The supplied code contains a simple test routine that gives you examples on how to instantiate a GameModel
, {[Board}} and test them.
It is reasonable to test your code by the following process:
- Instantiate a
GameModel
using the supplied dummyIViewAdapter
object. - Load a test output puzzle into the model and then save a reference to model's current board -- this is your reference output board
- Load a test input puzzle into the model.
- Run your desired operation.
- Get a reference to the model's current board -- this is the test output board.
- Use
assertEquals
to compare the output board to the reference board.
It is highly recommended that you start testing with 2x2 boards. Carefully construct SIMPLE boards that will test just the feature in question.
After you are satisfied with your tests on 2x2 boards THEN move on to 3x3 boards. Note: testing irreducible boards with choices that lead to unsolvable boards may be impossible on a 2x2 board.
The supplied code does NOT contain a full suite of test boards!
Extra credit
If you are attempting an extra credit task, put a note to such at the top of your GameModel
class. If you don't, the staff might not see it and grade it.
(10 pts) Incorporate the supplied GeneratePuzzle
utility capability into the main Sudoku solver, both in the view and the model, to enable the user to generate and solve any of the 50,000 supplied puzzles. Remember that the view and the model MUST be kept separate--the only way they can communicate is via IModelAdapter
and IViewAdapter
, their respective adapters. Neither GameFrame
nor GameModel
may contain a reference to the other! (It is actually possible to add this feature without modifying GameModel
at all, though you are not required to do this.)
(10 pts) As any seasoned Sudoku player knows, there are other reduction rubrics that can be applied to more quickly reduce a board. For instance, if an unsolved cell includes a value choice that no other unsolved cell in its cell contains, then the cell must have that value (this can be extended to a sub-set of values spread across multiple cells in a cell set). Can you incorporate additional reduction rubrics in a modular, flexible and extensible fashion?
(10 pts) Challenge! Come up with a Sudoku puzzle (any order) that your solver can solve but the staff's solution cannot!Restriction: Keep using the setElement method in findSolution and do not change the contract of the setElement or findSolution methods.
Submission
Submit via Owlspace a .zip
file containing all the files from the entire HW11 folder, including all the support code including those that you modified. Donand data. Don't forget to add as header to the PartialSolution GameModel
class, your names and idsIDs. Be sure to mention if you did any extra credit tasks too.