class Solution {
public:
    int firstUniqChar(string s) {
        int count[256] = {};

        for (char c : s) {
            count[c]++;
        }

        for (size_t i = 0; i < s.size(); ++i) {
            if (count[s[i]] == 1) {
                return i;
            }
        }

        return -1;
    }
};