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

class Solution {
    public int firstUniqChar(String s) {
        if(s == null || s.length() == 0)
            return -1;

        int[] count = new int[26];
        for(int i = 0; i < s.length(); i++) {
            count[s.charAt(i) - 'a']++;
        }
        for(int i = 0; i < s.length(); i++) {
            if(count[s.charAt(i) - 'a'] == 1)
                return i;
        }

        return -1;
    }
}