public class Queens {

	public static void main(String[] args) {
		Board board = new Board(8); //create new board
		System.out.println( explore(board, 1) ); //total

	}

	public static int explore(Board board, int row) {
		int total = 0;
		//Base case: when no rows left
		if( row > board.size() ) {
			board.print();
			System.out.println();
			return 1;
		//Recursive case
		} else {
			for(int i = 1; i <= board.size(); i++) {
				if( board.safe(row, i) ) { //check if target space is free
					board.place(row, i); //place piece
					total += explore(board, row + 1); //explore rest of decision tree
					board.remove(row, i); //remove piece to backtrack and explore other branches
				}
			}

		}
		return total;

	}

}