2-4

class Solution {
    public int firstUniqChar(String s) {
        int bestIndex = 1000000000;
        for (char c = 'a'; c <= 'z'; c++) {
            int first = s.indexOf(c);
            int last = s.lastIndexOf(c);
            if (first != -1 && first == last) {
                bestIndex = Math.min(bestIndex, first);
            }
        }
        if (bestIndex == 1000000000) bestIndex = -1;
        return bestIndex;
    }
}



class Solution {
    public int firstUniqChar(String s) {
        int freq[] = new int[26];
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            freq[c - 'a']++;
        }
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if (freq[c - 'a'] == 1) {
                return i;
            }
        }
        return -1;
    }
}



class Solution {
    public int firstUniqChar(String s) {
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if (s.indexOf(c) == s.lastIndexOf(c)) {
                return i;
            }
        }
        return -1;
    }
}