Leetcode: Valid Anagram

Given two strings s and t, write a function to determine if t is an anagram of s.

For example,
s = "anagram", t = "nagaram", return true.
s = "rat", t = "car", return false.

Note:
You may assume the string contains only lowercase alphabets.

Follow up:
What if the inputs contain unicode characters? How would you adapt your solution to such case?

 1 public class Solution {
 2     public boolean isAnagram(String s, String t) {
 3         if (s==null || t==null || s.length()!=t.length()) return false;
 4         char[] ss = s.toCharArray();
 5         char[] tt = t.toCharArray();
 6         Arrays.sort(ss);
 7         Arrays.sort(tt);
 8         for (int i=0; i<ss.length; i++) {
 9             if (ss[i] != tt[i]) return false;
10         }
11         return true;
12     }
13 }