Вопрос по теме цикла фор

 import collections 
s = input() 
for k, v in collections.Counter(s).most_common(): 
    if v == 1: break 
    s = s.replace(k, '') 
print(s) 

 #include <iostream>
#include <map>

using namespace std;

int main() {
    string s, r;
    getline(cin, s);

    map<char, int> t;
    for (auto ch: s) { ++t[ch]; }
    for (auto ch: s) { if (t[ch] < 2) { r += ch; } }
    cout << r;
}