题解 | #字符统计#

##利用map，set树的自动排序，效率略有提高

#include <iostream>
#include <map>
#include <set>
using namespace std;

int main() {
    char a;
    map<char,int > st;
    map<int,set<char> > st2;

    while (cin >> a ) {
        ++st[a];
    }

    for(auto ite = st.begin();ite != st.end();++ite){
        st2[ite->second].insert(ite->first);
    }

    for(auto ite = st2.rbegin();ite != st2.rend();++ite){
        for(auto ite2= ite->second.begin(); ite2 != ite->second.end(); ++ite2){
            cout<<*ite2;
        }
    }
}