Sudoku Recursion Issue (Java)

Question

I'm having an issue with creating a random Sudoku grid. I tried modifying a recursive pattern that I used to solve the puzzle. The puzzle itself is a two dimensional integer array. This is what I have (By the way, the method doesn't only randomize the first row. I had an idea to randomize the first row, then just decided to do the whole grid):

public boolean randomizeFirstRow(int row, int col){
    Random rGen = new Random();

    if(row == 9){
        return true;
    }
    else{
        boolean res;
        for(int ndx = rGen.nextInt() + 1; ndx <= 9;){

            //Input values into the boxes
            sGrid[row][col] = ndx;
            //Then test to see if the value is valid
            if(this.isRowValid(row, sGrid) && this.isColumnValid(col, sGrid) && this.isQuadrantValid(row, col, sGrid)){
                // grid valid, move to the next cell
                if(col + 1 < 9){
                    res = randomizeFirstRow(row, col+1);
                }

                else{
                    res = randomizeFirstRow( row+1, 0);
                }

                //If the value inputed is valid, restart loop
                if(res == true){
                    return true;
                }
            }
        }
    }

    //If no value can be put in, set value to 0 to prevent program counting to 9
    setGridValue(row, col, 0);
    //Return to previous method in stack
    return false;
}

This results in an ArrayIndexOutOfBoundsException with a ridiculously high or low number (+- 100,000). I've tried to see how far it goes into the method, and it never goes beyond this line:

if(this.isRowValid(row, sGrid) && this.isColumnValid(col, sGrid) && this.isQuadrantValid(row, col, sGrid))

I don't understand how the array index goes so high. Can anyone help me out?

Jason S · Accepted Answer · 2011-01-13 02:49:54Z

3

 for(int ndx = rGen.nextInt() + 1; ndx <= 9;){

This looks fishy. Random.nextInt() returns a random integer within the integer's full range, not just from 0 to 9.

answered Jan 13, 2011 at 2:49

Jason S

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2 Comments

SkylineAddict Over a year ago

Okay, so I fixed that, but it's just returning zeros. I saw on a board that I am supposed to use random indexes instead of random input values. If it's not too much to ask for, could you show me how to implement that? Thanks a bunch.

Jason S Over a year ago

I don't understand what you are asking, you need to be more specific.

Haozhun · Accepted Answer · 2011-01-13 03:02:34Z

0

You'll want this.

public int nextInt(int n) Returns: a pseudorandom, uniformly distributed int value between 0 (inclusive) and n (exclusive).

answered Jan 13, 2011 at 3:02

Haozhun

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