String Permutation

	/**
	 * String permutation
	 * 
	 * e.g.
	 * 
	 * Input:
	 * 		abc
	 * 
	 * Output:
	 * 		abc  bac  cba  
	 * 		abc  acb  bac  bca  cab  cba
	 * 
	 * */