public void dfs(int col, int[] queen, int n) {
		if (col > n) {
			num++;
			return;
		}
		for (int i = 1; i <= n; i++) {
			if (isValid(i, col, queen)) {
				queen[col] = i;
				dfs(col + 1, queen, n);
				queen[col] = 0;

			}

		}
	}