I did this Sudoku solver for a school project and I’ve now decided to release it as a proof-of-concept project. It’s nothing fancy. It contains a class used to brute force Sudoku puzzles, you can read more about the algorithm on Wikipedia, and a little Swing GUI. I’ve never used Swing before doing this project so don’t expect anything amazing. The code is released under GPL v2 and I hope it might be useful to someone out there. There is a generated Javadoc so check it out for more detailed info about the classes.
Check out the code in my public Mercurial repository.
And heres a overview of the brute force class (got to the Mercurial repository to get the GUI source):
/**
* Sudoku Solver Proof-of-concept.
* Copyright (C) 2011 Anton Fagerberg (Kung Foo Code).
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package sudoku;
public class Sudoku {
private int[][] matrix = new int[9][9];
private int[][] inputMatrix = new int[9][9];
/**
* Remove all the numbers from the sudoku-matrixes.
*/
public void resetMatrix() {
matrix = new int[9][9];
inputMatrix = new int[9][9];
}
/**
* Set value of the X- & Y-coordinate in the matrix.
* If x > 8 the y-value will automatically increase. set(0, 1, 1) is the same as set(9, 0, 1).
* @param x X-coordinate, 0-80.
* @param y Y-coordinate, 0-8.
* @param value Number, 1,9.
*/
private void fill(int x, int y, int value) {
while (x < 0) {
x += 9;
y--;
}
while(x > 8) {
x -= 9;
y++;
}
matrix[x][y] = value;
}
/**
* Save value from user input to the matrix which handles user input.
* If x > 8 the y-value will automatically increase. set(0, 1, 1) is the same as set(9, 0, 1).
* @param x X-coordinate, 0-80.
* @param y Y-coordinate, 0-8.
* @param value Number, 1,9.
*/
public void set(int x, int y, int value) {
while (x < 0) {
x += 9;
y--;
}
while(x > 8) {
x -= 9;
y++;
}
inputMatrix[x][y] = value;
}
/**
* Copy the values of the matrix containing the user input to the matrix used when trying to solve the puzzle.
*/
private void copyMatrix() {
for (int x = 0; x != 9; x++)
for (int y = 0; y != 9; y++)
matrix[x][y] = inputMatrix[x][y];
}
/**
* Try to solve the sudoku-puzzle.
* @return True or false based on if the puzzle was solved or not.
*/
public boolean solve() {
copyMatrix();
return solve(0);
}
/**
* Get the value from the specified X- & Y-coordinate in the matrix used to solve the sudoku-puzzles.
* If x > 8 the y-value will automatically increase. set(0, 1, 1) is the same as set(9, 0, 1).
* @param x X-coordinate, 0-80.
* @param y Y-coordinate, 0-8.
* @return The value, 0-9. (0 is regarded as not defined).
*/
public int getValue(int x, int y) {
while (x < 0) {
x += 9;
y--;
}
while(x > 8) {
x -= 9;
y++;
}
return matrix[x][y];
}
/**
* Get the value from the specified X- & Y-coordinate from the matrix which contain the user inputs.
* If x > 8 the y-value will automatically increase. set(0, 1, 1) is the same as set(9, 0, 1).
* @param x X-coordinate, 0-80.
* @param y Y-coordinate, 0-8.
* @return The value, 0-9. (0 is regarded as not defined).
*/
public int getValueOriginal(int x, int y) {
while (x < 0) {
x += 9;
y--;
}
while(x > 8) {
x -= 9;
y++;
}
return inputMatrix[x][y];
}
/**
* Recursive function which fills a valid number to the X- & Y-coordinate based on the sudoku-rules.
* The function will call itself with the next X- & Y-coordinate if it finds a valid number to insert or if the number is already set by the user input.
* If x > 8 the y-value will automatically increase.
* @param x X-coordinate.
* @return True or false if a valid number can be inserted or not.
*/
private boolean solve(int x) {
if (x == 81)
return true;
if (getValue(x, 0) != 0 && getValue(x, 0) == getValueOriginal(x, 0)) {
return solve(x+1);
}
else {
for (int i : getValidNumbers(x, 0)) {
if (i != 0) {
fill(x, 0, i);
if (!solve(x+1))
fill(x,0,0);
else
return true;
}
}
}
return false;
}
/**
* Validate if a specified number is valid at the X- & Y-coordinate based on the sudoku-rules.
* If x > 8 the y-value will automatically increase. set(0, 1, 1) is the same as set(9, 0, 1).
* @param x X-coordinate, 0-80.
* @param y Y-coordinate, 0-8.
* @param number Number (Only 1-9 can be valid).
* @return True or false based on if the number is valid according to the sudoku-rules.
*/
public boolean validNumberOriginal (int x, int y, int number) {
if (number < 1 || number > 9)
return false;
while (x < 0) {
x += 9;
y--;
}
while(x > 8) {
x -= 9;
y++;
}
int[] validNumbers = {1,2,3,4,5,6,7,8,9};
// Check vertical and horizontal
for (int i = 0; i != 9; i++) {
if (inputMatrix[i][y] != 0)
validNumbers[inputMatrix[i][y]-1] = 0;
if (inputMatrix[x][i] != 0)
validNumbers[inputMatrix[x][i]-1] = 0;
}
// Check the "squares"
int squareX, squareY;
if (x < 3)
squareX = 0;
else if (x < 6)
squareX = 3;
else
squareX = 6;
if (y < 3)
squareY = 0;
else if (y < 6)
squareY = 3;
else
squareY = 6;
for (int i = 0; i != 3; i++) {
for (int j = 0; j != 3; j++) {
if (inputMatrix[i+squareX][j+squareY] != 0) {
validNumbers[inputMatrix[i+squareX][j+squareY]-1] = 0;
}
}
}
return (validNumbers[number-1] == 0) ? false : true;
}
/**
* Returns an array of the valid numbers at the X- & Y-coordinate according to the sudoku-rules.
* If the number n is valid the array will have array[n-1] = n. If n is invalid array[n-1] = 0.
* If x > 8 the y-value will automatically increase. set(0, 1, 1) is the same as set(9, 0, 1).
* @param x X-coordinate, 0-80.
* @param y Y-coordinate, 0-8.
* @return Array of valid numbers (size 9).
*/
private int[] getValidNumbers(int x, int y) {
while (x < 0) {
x += 9;
y--;
}
while(x > 8) {
x -= 9;
y++;
}
int[] validNumbers = {1,2,3,4,5,6,7,8,9};
// Check vertical and horizontal
for (int i = 0; i != 9; i++) {
if (matrix[i][y] != 0) {
validNumbers[matrix[i][y]-1] = 0;
}
if (matrix[x][i] != 0) {
validNumbers[matrix[x][i]-1] = 0;
}
}
// Check the "squares"
int squareX, squareY;
if (x < 3)
squareX = 0;
else if (x < 6)
squareX = 3;
else
squareX = 6;
if (y < 3)
squareY = 0;
else if (y < 6)
squareY = 3;
else
squareY = 6;
for (int i = 0; i != 3; i++) {
for (int j = 0; j != 3; j++) {
if (matrix[i+squareX][j+squareY] != 0) {
validNumbers[matrix[i+squareX][j+squareY]-1] = 0;
}
}
}
return validNumbers;
}
/**
* Print a ascii-version of the sudoku-puzzle to the console.
*/
public void printTable() {
System.out.print("\n");
for (int x = 0; x != 9; x++) {
for (int y = 0; y != 9; y++) {
System.out.print(" " + inputMatrix[x][y] + " ");
if (y == 2 || y == 5)
System.out.print("|");
}
if (x == 2 || x == 5)
System.out.print("\n---------+---------+--------");
System.out.print("\n");
}
}
}