Question

Working on the N-queens problem. Having some difficult filling up the stack correctly. Was hoping anyone could give me any pointers.

Right now my output is strange..There are only 7 nodes, but my ‘success’ boolean needs 8 for it to be true. And the head node is 2,1 when I thought it should be 1,2 since I’d be increasing the column.

I know I need to check for the diagonal also, but I’m taking it step by step.

The first thing I need to work out if my conflictCheck method. It never return true (for, yes there is a conflict). I’ll update shortly if I figure something out.

Hurray
8, 1
7, 1
6, 1
5, 1
4, 1
3, 1
2, 1

EDIT:

I’ve made some changes to the code for a more recursive attempt.
My new output is this:

The stack
1, 1

End of stack
Pushing next node
The stack
2, 1
1, 1

End of stack
Moving over one column
The stack
2, 2
1, 1

End of stack
problem
Moving over one column
The stack
2, 3
1, 1

End of stack

This is part of the code/work in progress. Right now, it’s running into an eternal loop, most likely from that while (conflictCheck)

    public static boolean conflictCheck() {
    QueenNode temp = head;
    //walk through stack and check for conflicts

    while(temp!=null) {
        //if there is no next node, there is no conflict with it
        if (temp.getNext() == null){
            System.out.println("No next node");
            if (queens.size() < 8 ) {
                return false;
            }
        }
        else if (temp.getRow() ==temp.getNext().getRow() || temp.getColumn() == temp.getNext().getColumn() ||
                diagonal(temp, temp.getNext())){
            return true;
        }
    }
    return false;
}

public static void mover(QueenNode n) {
    System.out.println("Moving over one column");

        n.setColumn(n.getColumn()+1);

    queens.viewPieces();
}

public static void playChess(int k, int total) {
    QueenNode temp= head;
    while (temp != null) {
        System.out.println("Pushing next node");

        queens.push(k,1);
        queens.viewPieces();
        //success
        if(k == 8){
            System.out.println("Hurray");
            success = true;
            return;
        }
        //conflict between pieces, loops through entire board
        while (conflictCheck()) {
            if (head.getColumn() != 8) {
                mover(head);
            }
            else {
                queens.pop();
                mover(head);
            }
        }

        playChess(k+1, total);                  
    }
}

public static void main(String[] args) {
    queens.push(1, 1);
    queens.viewPieces();
    success = false;
    playChess(2, total);
}

}

Answer 1

temp != null && temp.getNext()!= null – for 8th queen the value temp.getNext() is null and it is not printed. Change to:

while (temp != null ) {
                System.out.println(temp.getRow() + ", " + temp.getColumn());
                temp = temp.getNext();
            }

---

Edit

Change || to &&:

if (temp.getRow() != temp.getNext().getRow() &&
                temp.getColumn() != temp.getNext().getColumn()) {
            return false;
        }

In code queens.push(queens.size()+1, 1); you always assign 1 as second argument. You should check all possibilities.