C++ 代码

    #include <bits/stdc++.h>
    using namespace std;
    int ch[26];

    int main(){
        string s; cin >> s;
        for(auto x:s) ch[int(x-'a')]++;
        for(auto x:s){
            if(ch[x-'a']==1) {
                cout << x;
                return 0;
            }
        }
        cout << "no" << endl;
    }