Backtracking - Generate Sudokuarray

Question

i want to generate a simple Sudokugenerator using backtrack. I am stuck / don't know if i used backtracking properly. zahlIstGueltigAufPosition returns if the number zahl is valid (if zahl appears once in the row/column or one of the 9 Boxes).

public static boolean fuelleArray(int y, int x, int zahl){

    sudokuArray[y][x]=zahl;


    if(zahlIstGueltigAufPosition(y,x,zahl)){

        if(x==8 && y<=7 && fuelleArray(y+1,0,1)){
            return true;

        }else if(x==8 && y==8 && fuelleArray(y,x,zahl)) {
            return true;

        }else if(x<=7 && y<=8){
            if(fuelleArray(y,x+1,1)) {
                return true;
            }
       }
    }else{
        if(zahl<9 && x<=8 && y<=8 ){fuelleArray(y,x,zahl+1);}
    }

    return false;
}

The Program gives out:

 1 2 3 4 5 6 7 8 9
 4 5 6 1 2 3 9 0 0
 0 0 0 0 0 0 0 0 0
 0 0 0 0 0 0 0 0 0
 0 0 0 0 0 0 0 0 0
 0 0 0 0 0 0 0 0 0
 0 0 0 0 0 0 0 0 0
 0 0 0 0 0 0 0 0 0
 0 0 0 0 0 0 0 0 0

Thanks for any help

First of all, please format your code. I can't read it with such an absence of spaces. Second of all, you've not told us what is wrong with this code. Please [edit] your question to provide this information. — Joe C, Jan 14 '18 at 22:10
Please edit your question to include a [specific programming problem](https://stackoverflow.com/help/how-to-ask). — Micheal O'Dwyer, Jan 14 '18 at 22:23

score 0 · Accepted Answer · answered Jan 24 '18 at 22:39

So this is my solution, there are better ways you can use backtracking to generate sudoku, like just calling fuelleArray(fieldIndex, numberInField). With that, backtracking would be more visible and clear in the code and you won't have to deal, like I had, with the cases when its on the end of a row.

public static boolean fuelleArray(int y, int x, int zahl){

    sudokuArray[y][x]=zahl;

    if(zahlIstGueltigAufPosition(y,x,zahl)){
                                       //#1
        if(x==8 && y<=7){              //if you aren't at the end
            if(fuelleArray(y+1,0,1)){  //look if the the next field
                return true;           //is correct
            }
                                       //#2
        }else if(x==8 && y==8){        //if I am at the end 
            return true;               //return true, cause at 
                                       //zahlIstGueltigAufPosition
                                       //we know its correctly plassed               
                                       //by the SudokuRules


        }else if(x<=7 && y<=8){        //Just like #1, but there it
            if(fuelleArray(y,x+1,1)){  //was to handle the end of a 
                return true;           //row

            }
        }
    }

    if(zahl<9 && x<=8 && y<=8 ){      //if we are not correct we
        if(fuelleArray(y,x,zahl+1)){  //increase the number in that
            return true;              //field

        }
    }else {                           //if we are at number 9 we put 
        sudokuArray[y][x]=0;          //put it back to zero
                                      //
    }                                 //
    return false;                     //and return false

}

Backtracking - Generate Sudokuarray

1 Answers1