static Set<String> set = new HashSet<>();

public static void main(String[] args) {
	permutations("abcd",0,3);
}
static void permutations(String s,int l, int r) {
	if(l==r) {
		if(set.contains(s)) return;
		set.add(s);
		System.out.println(s);
		return;
	}
	
		for(int i=l;i<=r;i++) {
			s=interchangeChar(s,l,i);
			permutations(s,l+1,r);
			s=interchangeChar(s,l,i);
		}
	}
		static String interchangeChar(String s,int a,int b) {
		char array[]=s.toCharArray();
		char temp=array[a];
		array[a]=array[b];
		array[b]=temp;
		return String.valueOf(array);
	}