NC97 字符串出现次数的TopK问题

网友答案

class Solution {
public:
    /**
     * return topK string
     * @param strings string字符串vector strings
     * @param k int整型 the k
     * @return string字符串vector<vector<>>
     */
    struct cmp{
        bool operator() (const pair<string, int> &p1, const pair<string, int> &p2)
        {
            return p1.second > p2.second || (p1.second == p2.second && p1.first < p2.first);
        }
    };
    vector<vector<string> > topKstrings(vector<string>& strings, int k) {
        // write code here
        vector<vector<string> > res;
        if(strings.size() == 0)
            return res;
        
        unordered_map<string, int> hash;
        for(auto c : strings)
            hash[c] ++;
        
        priority_queue<pair<string, int>, vector<pair<string, int>>, cmp> q;
        int i = 0;
        for(auto c : hash)
        {
            if(i < k) q.push(c);
            else
            {
                if(c.second > q.top().second || (c.second == q.top().second && c.first < q.top().first))
                {
                    q.pop();
                    q.push(c);
                }
            }
            i++;
        }
        while(!q.empty())
        {
            res.push_back({q.top().first, to_string(q.top().second)});
            q.pop();
        }
        
        reverse(res.begin(), res.end());
        return res;
    }
};