public static ArrayList<String[]> solveNQueens(int n) {
		if (n < 1)
			return null;
		result = new ArrayList<String[]>();
		int[] queens = new int[n + 1];
		for (int i = 1; i <= n; i++) {
			queens = new int[n + 1];
			queens[1] = i;
			dfs(2, n, queens);
		}
		return result;
	}