[sword finger offer] interview question 50: the first character that appears only once - hash table lookup

class Solution {
    
public:
    char firstUniqChar(string s) {
    
        //unordered_map<char, int> freq;
        int freq[256]= {
    0};
        for(char ele: s) 
            freq[ele]++;
        for(char ele: s)
            if(freq[ele]== 1) 
                return ele;
        return ' ';
    }
};