class Solution {

    public List<List<String>> groupAnagrams(String[] strs) {

        HashMap<String, List<String>> map = new HashMap<>();

        if(strs == null || strs.length == 0){

            return new ArrayList<List<String>>();

        }

        for(String str : strs){

            int[] arr = new int[26];

            for(int i = 0; i < str.length(); i++){

                arr[str.charAt(i) - 'a']++;

            }

            String key = Arrays.toString(arr);

            List<String> tempList = map.getOrDefault(key, new ArrayList<String>());

            tempList.add(str);

            map.put(key, tempList);

        }

        return new ArrayList<List<String>>(map.values());

    }

}

class Solution {

    public boolean isScramble(String s1, String s2) {

        if(s1.equals(s2)) return true;

        int[] letters = new int[26];

        for(int i = 0; i < s1.length(); i++){

            letters[s1.charAt(i) - 'a']++;

            letters[s2.charAt(i) - 'a']--;

        }

        for(int i = 0; i < 26; i++){

            if(letters[i] != 0) return false;

        }

        for(int i = 1; i < s1.length(); i++){

            if(isScramble(s1.substring(0, i), s2.substring(0, i))

               && isScramble(s1.substring(i), s2.substring(i))) return true;

            if(isScramble(s1.substring(0, i), s2.substring(s2.length() - i))

              && isScramble(s1.substring(i), s2.substring(0, s2.length() - i))) return true;

        }

        return false;

    }

}