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Sudoku.java
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Sudoku.java
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public class Sudoku {
// we define a simple grid to solve. Grid is stored in a 2D Array
public static int[][] GRID_TO_SOLVE = {
{9,0,0,1,0,0,0,0,5},
{0,0,5,0,9,0,2,0,1},
{8,0,0,0,4,0,0,0,0},
{0,0,0,0,8,0,0,0,0},
{0,0,0,7,0,0,0,0,0},
{0,0,0,0,2,6,0,0,9},
{2,0,0,3,0,0,0,0,6},
{0,0,0,2,0,0,9,0,0},
{0,0,1,9,0,4,5,7,0},
};
private int[][] board;
public static final int EMPTY = 0; // empty cell
public static final int SIZE = 9; // size of our Sudoku grids
public Sudoku(int[][] board) {
this.board = new int[SIZE][SIZE];
for (int i = 0; i < SIZE; i++) {
for (int j = 0; j < SIZE; j++) {
this.board[i][j] = board[i][j];
}
}
}
// we check if a possible number is already in a row
private boolean isInRow(int row, int number) {
for (int i = 0; i < SIZE; i++)
if (board[row][i] == number)
return true;
return false;
}
// we check if a possible number is already in a column
private boolean isInCol(int col, int number) {
for (int i = 0; i < SIZE; i++)
if (board[i][col] == number)
return true;
return false;
}
// we check if a possible number is in its 3x3 box
private boolean isInBox(int row, int col, int number) {
int r = row - row % 3;
int c = col - col % 3;
for (int i = r; i < r + 3; i++)
for (int j = c; j < c + 3; j++)
if (board[i][j] == number)
return true;
return false;
}
// combined method to check if a number possible to a row,col position is ok
private boolean isOk(int row, int col, int number) {
return !isInRow(row, number) && !isInCol(col, number) && !isInBox(row, col, number);
}
// Solve method. We will use a recursive BackTracking algorithm.
// we will see better approaches in next video :)
public boolean solve() {
for (int row = 0; row < SIZE; row++) {
for (int col = 0; col < SIZE; col++) {
// we search an empty cell
if (board[row][col] == EMPTY) {
// we try possible numbers
for (int number = 1; number <= SIZE; number++) {
if (isOk(row, col, number)) {
// number ok. it respects sudoku constraints
board[row][col] = number;
if (solve()) { // we start backtracking recursively
return true;
} else { // if not a solution, we empty the cell and we continue
board[row][col] = EMPTY;
}
}
}
return false; // we return false
}
}
}
return true; // sudoku solved
}
public void display() {
for (int i = 0; i < SIZE; i++) {
for (int j = 0; j < SIZE; j++) {
System.out.print(" " + board[i][j]);
}
System.out.println();
}
System.out.println();
}
public static void main(String[] args) {
Sudoku sudoku = new Sudoku(GRID_TO_SOLVE);
System.out.println("Sudoku grid to solve");
sudoku.display();
// we try resolution
if (sudoku.solve()) {
System.out.println("Sudoku Grid solved with simple BT");
sudoku.display();
} else {
System.out.println("Unsolvable");
}
}
}