387. First Unique Character in a String.cpp

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