451. Sort Characters By Frequency

https://leetcode.com/problems/sort-characters-by-frequency/description/

class Solution {
public:
    string frequencySort(string s) {
        map<char,int> m;
        for (auto c : s) 
            m[c]++;
        
        priority_queue<pair<int,char>> q;
        for (const auto& f : m)
            q.push( {f.second, f.first} );
        
        string res;
        while (!q.empty()) {
            res += string(q.top().first, q.top().second);
            q.pop();
        }
        return res;
    }
};