算法1

(哈希表) $O(n)$

C++ 代码

class Solution {
public:
    char firstNotRepeatingChar(string s) {
        unordered_map<char, int>map;
        for(auto x : s)
        {
            map[x]++;
        }
        char res = '#';
        for(auto x: s){
            if(map[x] == 1)
           { res = x;
            return res;}
        }
        return res;


    }
};