387-first-unique-character-in-a-string.cpp

class Solution {
public:
    int firstUniqChar(string s) {
        map <char, int> m;
        for (int i=0; i<s.length(); i++){
            m[s[i]]++;
        }
        for (int i=0; i<s.length(); i++){
            if (m[s[i]]==1)
                return i;
        }
        return -1;
    }
};