Add sudoku algorithm in Java

Author: danielabrozzoni

BackTracking/SudokuAlgorithm/Sudoku.java

@@ -0,0 +1,133 @@
+public class Sudoku {
+
+    public final int SUDOKU_SIZE = 9;
+    public final int UNASSIGNED = 0;
+
+
+    private int unassignedPositionRow;
+    private int unassignedPositionColumn;
+    private int[][] matrix = new int[SUDOKU_SIZE][SUDOKU_SIZE];
+
+    public Sudoku() {
+
+        clear();
+    }
+
+    public void clear() {
+        for(int i = 0; i < SUDOKU_SIZE; i++)
+            for(int j = 0; j < SUDOKU_SIZE; j++)
+                matrix[i][j] = UNASSIGNED;
+    }
+
+    public void insertRandomNumbers(int n) {
+
+        for(int i = 0; i < n; i++) {
+            int randomRow = (int)(Math.random() * (SUDOKU_SIZE - 1));
+            int randomColumn = (int)(Math.random() * (SUDOKU_SIZE - 1));
+            int randomNumber = (int)(Math.random() * (SUDOKU_SIZE - 1) + 1);
+            matrix[randomRow][randomColumn] = randomNumber;
+        }
+    }
+
+    public boolean solve() {
+
+        if(!findUnassignedPosition())
+            return true;
+
+        for(int n = 1; n <= SUDOKU_SIZE; n++) {
+
+            if(canBePlaced(unassignedPositionRow, unassignedPositionColumn, n)) {
+                final int i = unassignedPositionRow;
+                final int j = unassignedPositionColumn;
+                matrix[i][j] = n;
+
+                if(solve())
+                    return true;
+
+                matrix[i][j] = UNASSIGNED;
+            }
+        }
+
+        return false;
+    }
+
+    private boolean findUnassignedPosition() {
+
+        for(int i = 0; i < SUDOKU_SIZE; i++) {
+            for(int j = 0; j < SUDOKU_SIZE; j++) {
+                if(matrix[i][j] == UNASSIGNED) {
+                    unassignedPositionRow = i;
+                    unassignedPositionColumn = j;
+                    return true;
+                }
+            }
+        }
+
+        return false;
+    }
+
+    private boolean canBePlaced(int row, int column, int number) {
+
+        return !isUsedInRow(row, number) && !isUsedInColumn(column, number) && !isUsedInBox(row, column, number);
+    }
+
+    private boolean isUsedInRow(int row, int number) {
+
+        for(int i = 0; i < SUDOKU_SIZE; i++)
+            if(matrix[row][i] == number)
+                return true;
+        return false;
+    }
+
+    private boolean isUsedInColumn(int column, int number) {
+
+        for(int i = 0; i < SUDOKU_SIZE; i++)
+            if(matrix[i][column] == number)
+                return true;
+        return false;
+    }
+
+    private boolean isUsedInBox(int row, int column, int number) {
+
+        int startRow = row - row % 3;
+        int startColumn = column - column % 3;
+
+        for(int i = 0; i < 3; i++)
+            for(int j = 0; j < 3; j++)
+                if(matrix[startRow + i][startColumn + j] == number)
+                    return true;
+        return false;
+    }
+
+    public void print() {
+        System.out.println("-------------------------");
+
+        for(int i = 0; i < SUDOKU_SIZE; i++) {
+            for (int j = 0; j < SUDOKU_SIZE; j++) {
+                if (j == 0)
+                    System.out.print("| ");
+                System.out.print(matrix[i][j] + " ");
+                if (j % 3 == 2)
+                    System.out.print("| ");
+
+            }
+            System.out.println();
+            if(i % 3 == 2)
+                System.out.println("-------------------------");
+        }
+        
+    }
+
+    public static void main(String[] args) {
+
+        Sudoku sudoku = new Sudoku();
+        sudoku.insertRandomNumbers(3);
+        System.out.println("Current sudoku state:");
+        sudoku.print();
+        System.out.println("Solving...");
+        if(sudoku.solve())
+            sudoku.print();
+        else
+            System.out.println("No solution found! :(");
+    }
+}