1 public boolean isScramble(String s1, String s2) {
 2         if (s1.length() != s2.length()) {
 3             return false;
 4         }
 5         if (s1.equals(s2)){
 6             return true;
 7         }
 8         int n = s1.length();
 9         int[] chars = new int[26];
10         for (int i = 0; i < n; i++) {
11             chars[s1.charAt(i) - ‘a‘]++;
12             chars[s2.charAt(i) - ‘a‘]--;
13         }
14         for (int i = 0; i < 26; i++) {
15             if (chars[i] != 0) {
16                 return false;
17             }
18         }
19         for (int i = 1; i < n; i++) {
20             if (isScramble(s1.substring(0, i), s2.substring(0, i)) 
21                 && isScramble(s1.substring(i), s2.substring(i))) {
22                 return true;
23             }
24             if (isScramble(s1.substring(0, i), s2.substring(n - i)) && isScramble(s1.substring(i), s2.substring(0, n - i))) {
25                 return true;
26             }
27         }
28         return false;
29     }