Top K Frequent Elements (C++ Top K Frequent Elements)

Problem-solving ideas:

(1) Use map to store key-value pairs, and use vector to customize sorting

class Solution {
public:
    vector<int> topKFrequent(vector<int>& nums, int k) {
        unordered_map<int,int> mp;
        for(int i=0;i<nums.size();i++) {
            mp[nums[i]]++;
        }
        
        vector<pair<int,int>> vec;
        for(auto it=mp.begin();it!=mp.end();it++) {
            vec.push_back({it->first,it->second});
        }
        auto comp=[&](const pair<int,int> &a,const pair<int,int> &b) {
            if(a.second>=b.second) return true;
            else return false;
        };
        
        sort(vec.begin(),vec.end(),comp);
        
        vector<int> v;
        for(int i=0;i<k;i++) {
            v.push_back(vec[i].first);
        }
        return v;
    }
};