Solution.java

class Solution {
    public boolean isScramble(String s1, String s2) {
        if(s1.equals(s2)) return true;
        if(s1.length()!=s2.length()) return false;
        int len = s1.length();
        int[] count = new int[26];
        for(int i = 0; i < len; i++){
            count[s1.charAt(i) - 'a']++;
            count[s2.charAt(i) - 'a']--;
        }
        for(int item : count) if (item != 0) return false;
        for(int i = 1; i <= len - 1; 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(len - i)) &&
                    isScramble(s1.substring(i), s2.substring(0, len - i)))
                return true;
        }
        return false;
    }
}