Leetcode-692 Top K Frequent Words(前K个高频单词)

struct cmp
{
    bool operator()(const pair<string,int> p1, const pair<string,int> p2)
    {
        if(p1.second!=p2.second)
            return p1.second > p2.second; //second的小值优先
        return p1.first < p2.first;
    }
};

class Solution
{
    public:
        vector<string> topKFrequent(vector<string>& words, int k)
        {
            unordered_map<string,int> mymap;
            for(auto s:words)
            {
                auto ptr_to_str = mymap.find(s);
                if(ptr_to_str==mymap.end())
                {
                    mymap.insert(make_pair(s,1));
                }
                else
                {
                    ptr_to_str->second ++;
                }
            }

            priority_queue<pair<string,int>, vector<pair<string,int>>, cmp> Q;
            for(auto p:mymap)
            {
                if(Q.size()<k)
                {
                    Q.push(make_pair(p.first,p.second));
                }
                else
                {
                    if(p.second>Q.top().second || (p.second==Q.top().second && p.first<Q.top().first))
                    {
                        Q.pop();
                        Q.push(make_pair(p.first,p.second));
                    }
                }
            }

            vector<string> result;
            while(!Q.empty())
            {
                result.emplace_back(Q.top().first);
                Q.pop();
            }
            reverse(result.begin(),result.end());
            return result;
        }
};