Sudoku Solver debugging

Question

I know that there are a few posts like these before, but they aren't helping me. I am writing a program that can solve a sudoku. I found an algorithm here: http://www.heimetli.ch/ffh/simplifiedsudoku.html . I am trying to write it in java and starting with a console based program. It gets into an infinite loop for some reason, even though I have ways to stop it.

package sudokuSolver;

public class Solver {
static int[][] board;   //teh board
static boolean solved;          //if the sudoku is solved

public static void main(String[] args) throws Exception 
{
    //establish temporary board for now
    final int[][] TUE24JAN = {{0,0,9,0,0,0,8,0,0},
                              {0,1,0,0,2,0,0,3,0},
                              {0,0,0,7,0,8,0,0,0},
                              {2,0,0,0,8,0,0,0,7},
                              {0,3,0,1,0,2,0,4,0},
                              {4,0,0,0,7,0,0,0,5},
                              {0,0,0,6,0,3,0,0,0},
                              {0,8,0,0,9,0,0,7,0},
                              {0,0,6,0,0,0,9,0,0},};

    final int[][] WED25JAN = {{2,5,0,0,0,0,4,0,0},
                              {0,0,3,1,0,0,7,0,0},
                              {0,0,0,0,8,4,0,6,0},
                              {4,0,0,0,0,0,0,8,0},
                              {7,0,0,0,1,0,0,0,4},
                              {0,3,0,0,0,0,0,0,9},
                              {0,9,0,6,5,0,0,0,0},
                              {0,0,1,0,0,9,2,0,0},
                              {0,0,2,0,0,0,0,4,3},};

    board = TUE24JAN;
    solved = false;
    printBoard();

    solve(0,0);
    System.out.println("
");
    printBoard();
}

public static void solve(int x, int y) throws Exception
{
    //catches the end of the line
    if(y > 8)
    {
        y = 0;
        x++;
    }

    //catches the end of the board
    if(x > 8 || solved)
    {
        solved = true;
        return;
    }
    //put a number in the cell
    for(int i = 1; i < 10; i++)
    {
        if(!inRow(x, i) && !inCol(y, i) && !inBox(x, y, i) && !solved)
        {
            board[x][y] = i;
            solve(x, y+1);
            board[x][y] = 0;
        }
    }
}

//returns if the value is in the specified row
public static boolean inRow(int x, int val)
{
    for(int i = 0; i < 9; i++)
        if(board[x][i] == val)
            return true;
    return false;
}

//returns whether the value is in the specified column
public static boolean inCol(int y, int val)
{
    for(int i = 0; i < 9; i++)
        if(board[i][y] == val)
            return true;
    return false;
}

//returns whether the value fits based
public static boolean inBox(int x, int y, int val)
{
    int row = (x / 3) * 3;
    int col = (y / 3) * 3;
    for(int r = 0; r < 3; r++)
    for(int c = 0; c < 3; c++)
        if(board[row+r][col+c] == val)
            return true;
    return false;
}

public static void printBoard()
{

    for(int i = 0; i < 9; i++)
    {
        if( i % 3 == 0)
            System.out.println("----------------------");
        for(int j = 0; j < 9; j++)
        {
            if(j % 3 == 0)
                System.out.print("|");
            if(board[i][j] < 10 && board[i][j] > 0)
                System.out.print(board[i][j] + " ");
            else
                System.out.print("- ");
        }
        System.out.println("|");
    }
    System.out.print("----------------------
");
}

}

Edit: It should not clear the cells because when it finally reaches a solution, it changes solved to true which lets it know to not change anymore values. I am not getting a stack overflow error, it just keeps running. I accidentally let it run for an hour and it was still running, it just kept repeating at one point, never hit a solved state and never hit the first recursive sequence.

As for step by step debugging, you can do that? I use eclipse, but if there's a different IDE that allows you to do a line by line run-through, could you tell me?

Sudoku Solver debugging

Answers (1)

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