347. Top K Frequent Elements

Given a non-empty array of integers, return the k most frequent elements.

For example,
Given [1,1,1,2,2,3] and k = 2, return [1,2].

class Solution {
public:
    vector<int> topKFrequent(vector<int>& nums, int k) {
        unordered_map<int, int> hash;
        priority_queue<pair<int, int>> heap;
    
        vector<int> ret;
    
        for (int num : nums) {
            hash[num]++;
        }
    
        for (auto it : hash) {
            heap.push(make_pair(it.second, it.first));
        }
    
        for (int i = 0; i<k; i++) {
            ret.push_back(heap.top().second);
            heap.pop();
        }
        return ret;
    }
};