Everything seems to work fine in the algorithm besides the solve method. When it executes the program using a solvable Sudoku board, it says that it cannot be solved. I’ve tried everything I can think of in the solve method. I’ve tried debugging and it fails after the first row is tested. Any suggestions? Here is the full code so far:
public class SudokuSolver {
public static void initializeGrid(int[][] grid, int[][] puzzle) {
for (int r = 0; r < puzzle.length; r++) {
for (int c = 0; c < puzzle[0].length; c++) {
grid [r][c] = puzzle [r][c];
}
}
}
public static void displayGrid(int[][] grid) {
for (int r = 0; r < grid.length; r++) {
if (r % 3 == 0) {
System.out.println("+---+---+---+");
}
for (int c = 0; c < grid[r].length; c++) {
if (c % 3 == 0) {
System.out.print("|");
}
displayDigits(r, c, grid);
}
System.out.print("|");
System.out.println();
}
System.out.println("+---+---+---+");
}
if (grid[r][c] == 0) {
System.out.print(' ');
}
else {
System.out.print(grid[r][c]);
}
}
public static int getEmptyCells(int[][] grid, int[][] emptyCells) {
int i = 0;
int numEmptyCells = 0;
for (int r = 0; r < grid.length; r++) {
for (int c = 0; c < grid[r].length; c++) {
if (grid[r][c] == 0) {
emptyCells[i][0] = r;
emptyCells[i][1] = c;
numEmptyCells++;
i++;
}
}
}
return numEmptyCells;
}
private static boolean hasNoDuplicates(int[] digitsList) {
for (int j = 0; j < digitsList.length; j++) {
for (int k = j + 1; k < digitsList.length; k++) {
if (digitsList[j] == digitsList[k] && digitsList[j] != 0)
return false;
}
}
return true;
}
private static boolean checkCurrentRow(int[][] grid, int currentRow) {
int[] digitsList = new int[grid.length];
for (int c = 0; c < digitsList.length; c++) {
digitsList[c] = grid[currentRow][c];
}
if (hasNoDuplicates(digitsList)) {
return true;
}
return false;
}
private static boolean checkCurrentCol(int[][] grid, int currentCol) {
int[] digitsList = new int[grid.length];
for (int i = 0; i < digitsList.length; i++) {
digitsList[i] = grid[i][currentCol];
}
if (hasNoDuplicates(digitsList)) {
return true;
}
return false;
}
private static boolean checkCurrentRegion(int[][] grid, int currentRow, int currentCol) {
int[] digitsList = new int[grid.length];
currentRow = (currentRow / 3) * 3;
currentCol = (currentCol / 3) * 3;
int i = 0;
for (int r = 0; r < 3; r++) {
for (int c = 0; c < 3; c++) {
digitsList[i] = grid[currentRow + r][currentCol + c];
i++;
}
}
if (hasNoDuplicates(digitsList)) {
return true;
}
return false;
}
public static boolean isConsistent(int[][] grid, int currentRow, int currentCol) {
if (checkCurrentRow(grid, currentRow) && checkCurrentCol(grid, currentCol)
&& checkCurrentRegion(grid, currentRow, currentCol)) {
return true;
}
return false;
}
public static boolean solvePuzzle(int[][] grid, int[][] emptyCells, int numEmptyCells) {
int i = 0;
int j = 0;
int currentCellDigit = grid[emptyCells[i][0]][emptyCells[i][1]];
while (j < numEmptyCells) {
if (currentCellDigit != 9) {
currentCellDigit++;
grid[emptyCells[i][0]][emptyCells[i][1]] = currentCellDigit;
if (isConsistent(grid, emptyCells[i][0], emptyCells[i][1])) {
grid[emptyCells[i][0]][emptyCells[i][1]] = currentCellDigit;
i++;
j++;
}
else {
grid[emptyCells[i][0]][emptyCells[i][1]] = currentCellDigit - 1;
}
}
else {
currentCellDigit = 0;
currentCellDigit = grid[emptyCells[i][0]][emptyCells[i][1]];
i--;
j--;
if (j < 0) {
return false;
}
}
}
return true;
}
public static void main(String[] args) {
final int SIZE = 9;
int[][] puzzle = { {0,2,9,0,0,3,0,0,5},
{5,0,7,0,0,0,0,9,0},
{6,0,0,0,0,9,4,2,0},
{3,0,2,0,0,4,0,0,0},
{0,0,5,0,3,0,7,0,0},
{0,0,0,5,0,0,6,0,2},
{0,9,8,4,0,0,0,0,3},
{0,3,0,0,0,0,1,0,6},
{2,0,0,3,0,0,9,4,0}
};
int[][] grid = new int[SIZE][SIZE];
int[][] emptyCellsList = new int[SIZE*SIZE][2];
int numEmptyCells = 0;
initializeGrid(grid, puzzle);
numEmptyCells = getEmptyCells(grid, emptyCellsList);
System.out.println("The puzzle:");
displayGrid(puzzle);
if (solvePuzzle(grid, emptyCellsList, numEmptyCells)) {
System.out.println("has been solved:");
displayGrid(grid);
}
else {
System.out.println("cannot be solved!");
}
}
}
Your initializeGrid is wrong. IMHO, it should be:
instead of
EDIT: my answer below this
It’s been indented properly (lesson 1) and arranged the curly braces accordingly (lesson 2). Learn to understand what you are trying to do line by line and when you are stuck on a specific line or method call, look for help (lesson 3). The code below will compile but will not (yet) solve the puzzle. Read and replace the comments inside solvePuzzle for me (lesson 4). Do some thinking and analyzing since this is your homework 😉 Good luck!
P.S. this will do backtracking if you’ve replaced the comments above with proper code.