692. Top K Frequent Words

class ComparisonClass {
public:
    bool operator() (pair<int,string> p1, pair<int,string> p2) {
        return p1.first < p2.first || p1.first == p2.first && p1.second > p2.second;
    }
};
class Solution {
public:
    vector<string> topKFrequent(vector<string>& words, int k) {
        unordered_map<string,int> freq;
        for (const auto& w : words)
            freq[w]++;
        priority_queue<pair<int,string>, vector<pair<int,string>>, ComparisonClass> q;
        for (const auto& f : freq)
            q.push( { f.second, f.first });
        
        vector<string> res;
        while (k-- > 0 && !q.empty()) {
            res.push_back(q.top().second);
            q.pop();
        }
        return res;
    }
};