First Unique Character in a String

Given a string, find the first non-repeating character in it and return it's index. If it doesn't exist, return -1.

Examples:

s = "leetcode"
return 0.

s = "loveleetcode",
return 2.

Note: You may assume the string contain only lowercase letters.

 class Solution {
     public int firstUniqChar(String s) {
         int freq[] = new int[];
         for (int i = ; i < s.length(); i++) {
             freq[s.charAt(i) - 'a']++;
         }

         for (int i = ; i < s.length(); i++) {
             if (freq[s.charAt(i) - 'a'] == ) {
                 return i;
             }
         }
         return -;
     }
 }