字符串全排列，并去重。

public class TestB {

	public static void permutation(String str,Set set){
		if(str==null) return;
		int len=str.length();
		if(len==0 || len==1)return;
		 permutation(str.toCharArray(), 0,set);

	}

	private static void permutation(char[] str, int i, Set set) {
		 if (i >= str.length)
	            return;
	        if (i == str.length - 1) {
	        //    System.out.println(String.valueOf(str));
	            set.add(String.valueOf(str));
	        } else {
	            for (int j = i; j < str.length; j++) {
	                char temp = str[j];
	                str[j] = str[i];
	                str[i] = temp;

	                permutation(str, i + 1,set);

	                temp = str[j];
	                str[j] = str[i];
	                str[i] = temp;
	            }
	        }

	}

	public static void main(String[] args) {
		   Set<String>set=new HashSet<>();
		   permutation("acda",set);
		   for(String s:set){
			   System.out.println(s);
		   }

	}

}