The beauty is we just need to scan the String s one time, and then for the 2nd pass we just iterate array of length 26. So this approach is good for input string with long length.

```
public class Solution {
public int firstUniqChar(String s) {
if (s == null || s.length() == 0) return -1;
int[] count = new int[26];
Arrays.fill(count, -1);
for (int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
if (count[c - 'a'] >= 0) count[c - 'a'] = -2;
else if (count[c - 'a'] == -1) count[c - 'a'] = i;
}
int min = s.length();
for (int i = 0; i < 26; i++) {
if (count[i] >= 0) min = Math.min(min, count[i]);
}
return min == s.length() ? -1 : min;
}
}
```