leetcode 347. 前 K 个高频元素

	class Solution {
public: 
    vector<int> topKFrequent(vector<int>& nums, int k) {
      unordered_map<int,int>F;
      vector<int>ans;
      vector<int>res(nums.size(),0);
      for(auto p:nums)
      F[p]++;
      for(auto p:F)res.push_back(p.second);
      sort(res.begin(),res.end(),[](int &a,int &b){return a>b;});
      int n=res[k-1]; 
      for(auto p:F)
      if(p.second>=n)
      ans.push_back(p.first);
   
      return ans;
    }
};