哈希表

class Solution {
public:
    unordered_map<int,int> st; //哈希表统计数据
    vector<pair<int,int>> a; //vector的sort来排序
    vector<int> topKFrequent(vector<int>& nums, int k) {
        int n = nums.size();
        vector<int> res;
        for(int i=0;i<n;i++){
            st[nums[i]] ++;
        }
        auto it = st.begin();
        while(it != st.end()) {
            a.push_back({it->second,it->first});
            it ++;
        }
        sort(a.begin(),a.end());
        for(int i = a.size()-1;i>=0;i--){
            if(k == 0) break;
            res.push_back(a[i].second);
            k--;
        }
        return res;
    }
};