permutation of a given string

	public class StringPermutation {
	public List<String> permute(char input[]) {
	Map<Character, Integer> countMap = new TreeMap<>();
	for (char ch : input) {
	countMap.compute(ch, (key, val) -> {
	if (val == null) {
	return 1;
	} else {
	return val + 1;
	}
	});
	}
	char str[] = new char[countMap.size()];
	int count[] = new int[countMap.size()];
	int index = 0;
	for (Map.Entry<Character, Integer> entry : countMap.entrySet()) {
	str[index] = entry.getKey();
	count[index] = entry.getValue();
	index++;
	}
	List<String> resultList = new ArrayList<>();
	char result[] = new char[input.length];
	permuteUtil(str, count, result, 0, resultList);
	return resultList;
	}
	public void permuteUtil(char str[], int count[], char result[], int level, List<String> resultList) {
	if (level == result.length) {
	resultList.add(new String(result));
	return;
	}
	for(int i = 0; i < str.length; i++) {
	if(count[i] == 0) {
	continue;
	}
	result[level] = str[i];
	count[i]--;
	permuteUtil(str, count, result, level + 1, resultList);
	count[i]++;
	}
	}
	private void printArray(char input[]) {
	for(char ch : input) {
	System.out.print(ch);
	}
	System.out.println();
	}
	public static void main(String args[]) {
	StringPermutation sp = new StringPermutation();
	sp.permute("AABC".toCharArray()).forEach(s -> System.out.println(s));
	}
	}