s = "leetcode"
return 0.
 
s = "loveleetcode",
return 2.

public class Solution {
    public int firstUniqChar(String s) {
        if (s == null || s.length() == 0) {
            return -1;
        }
        HashMap<Character, Integer> map = new HashMap<Character, Integer>();
        for (int i = 0; i < s.length(); i++) {
            Integer in = map.get(s.charAt(i));
            if (in == null) 
                map.put(s.charAt(i), 1);
            else
                map.put(s.charAt(i), 2);
        }
        for (int i = 0; i < s.length(); i++) {
            if(map.get(s.charAt(i)) == 2) {
                continue;
            } else {
                if (map.get(s.charAt(i)) == 1) {
                    return i;
                }
            }
        } 
        return -1;
    }
}