⌛⌛ Sudoku

There is material for this question in the remote material repository:

• The material is located in the round4/sudoku directory.

• SudokuTest.java: a test program to test your implementation.

• input.txt: a test input for the program.

• output.txt: an example output matching input.txt.

Exercise: Sudoku

The exercise is returned as a Maven project. Place the pom.xml file in the round4/sudoku directory of your local repository and create to this directory the src/main/java subdirectory. Create the class file Sudoku.java and attach it to the fi.tuni.prog3.sudoku package. Your files should be in the round4/sudoku/src/main/java/fi/tuni/prog3/sudoku directory. NetBeans creates the directory structure matching the package for this task automatically, provided that you enter correct values, when creating your Maven project.

Implement a Sudoku class that maintains a Sudoku grid and can, for example, check if it is legal. If you have somehow managed to avoid knowing what a Sudoku is, see first its Wikipedia article.

To be more precise, you should implement the Sudoku class to have the public members given below. All the other members should be private.

• Constructor Sudoku() that initializes the Sudoku object to hold a 9 × 9 Sudoku grid, all cells of which are empty. Empty cells are expressed using a space character ' '.

  • You are free to decide the internal (private) details of how you store the grid.

• Member function set(int i, int j, char c): sets the character c into the grid cell (i, j). By this we mean the cell in the column j of row i.

  • Both the rows and columns have index values from 0 to 8. The function must check that i and j are legal row and column indices. If this is not the case, the function prints a message of form “Trying to access illegal cell (i, j)!”.

  • A Sudoku grid is allowed to hold only space characters ' ' (empty cells) and the digit characters '1', '2', '3', '4', '5', '6', '7', '8' and '9'. If the value of the parameter c is some other character, it will not be set and a message of form “Trying to set illegal character c to (i, j)!” should be printed.

• Member function check(): checks if the current values in the Sudoku grid are legal. Returns true (is legal) or false (is not legal).

  • A Sudoku grid is legal if no row, column or 3 x 3 sub-block contains a digit multiple times (multiple spaces may naturally occur).

    • Check first the rows, then the columns and finally the sub-blocks (inspect the sub-blocks in a row-wise manner, starting with the upper left corner sub-block).

    • Record the smallest recurring digit from a row, column or sub-block. This ensures that the messages described below will be unique even if there were several recurring digits. When the smallest recurring digit has been found, print one of the messages desribed below and return immediately from the function with the false value.

      • Row: “Row i has multiple c's!”, where i is the row index.

      • Column: “Column j has multiple c's!”, where j is the column index.

      • Sub-block: “Block at (x, y) has multiple c's!”, where x and y are the row and column index of the upper left corner cell of the sub-block.

• Member function print(): prints the Sudoku grid. The grid borders are expressed using the characters '#', '-', '|' and '+' and each cell value has a space on its both sides. See the example output file for further details.

• All printing should be done using the System.out stream.

The automatic tests, and the ones given below, assume that you make the following definitions in your pom.xml project file:

• The value of artifactId is sudoku.

• The value of version is 1.0.

• The values of the maven.compiler.source and maven.compiler.target elements are 17 or lower. The grader uses Java 17, so any newer versions won’t work.

• A Onejar plugin definition where the value of mainClass is SudokuTest which is the name of the given test class (see below).

Testing

You can test your class with the test program given in the file SudokuTest.java, the test file called input.txt and the example output called output.txt.

Set SudokuTest.java into the root of the src/main/java subdirectory of your Maven project, and the other files into the root directory of your Maven project, that is, where the pom.xml is. Note that SudokuTest.java does not include a package definition and therefore is not placed into a deeper subdirectory.

After this you can compile the program with mvn package and run the test as java -jar target/sudoku-1.0.one-jar.jar input.txt in the root directory of the project. The test should produce the output depicted in the file output.txt.

Submitting

Submitting is done as usual by entering the URL of your personal remote directory in the field below.

A+ presents the exercise submission form here.

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