/**
	 * get the next permutation based on dictionary order method
	 * 
	 * @param cur
	 * @return next permutation string, or null if cur is the last
	 */
	public static String next(String cur) {
		String ret = null;
		if (cur == null)
			return ret;
		int strlen = cur.length();
		char[] lcur = cur.toLowerCase().toCharArray();
		int j = strlen - 2;
		while (j >= 0 && lcur[j] > lcur[j + 1]) {
			j--;
		}
		if (j < 0)
			return ret;

		int k = strlen - 1;
		while (lcur[k] < lcur[j]) {
			k--;
		}

		// swap lcur[k], lcur[j]
		char temp = lcur[k];
		lcur[k] = lcur[j];
		lcur[j] = temp;

		// reverse lcur[j+1, ..., strlen-1]
		int low = j + 1;
		int high = strlen - 1;
		while (low < high) {
			temp = lcur[low];
			lcur[low] = lcur[high];
			lcur[high] = temp;
			low++;
			high--;
		}
		ret = String.valueOf(lcur);
		return ret;
	}