<p>Given an integer array <code>nums</code> and an integer <code>k</code>, return <em>the</em> <code>k</code> <em>most frequent elements</em>. You may return the answer in <strong>any order</strong>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> nums = [1,1,1,2,2,3], k = 2
<strong>Output:</strong> [1,2]
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> nums = [1], k = 1
<strong>Output:</strong> [1]
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 10<sup>5</sup></code></li>
	<li><code>-10<sup>4</sup> &lt;= nums[i] &lt;= 10<sup>4</sup></code></li>
	<li><code>k</code> is in the range <code>[1, the number of unique elements in the array]</code>.</li>
	<li>It is <strong>guaranteed</strong> that the answer is <strong>unique</strong>.</li>
</ul>

<p>&nbsp;</p>
<p><strong>Follow up:</strong> Your algorithm&#39;s time complexity must be better than <code>O(n log n)</code>, where n is the array&#39;s size.</p>

class Solution {
public:
struct cmp{
    bool operator()(const pair<int,int>& x, pair<int,int>& y ){
        return x.second>y.second;  //Min Heap
    }
};
    vector<int> topKFrequent(vector<int>& nums, int k) {
        priority_queue<pair<int,int>,vector<pair<int,int>>,cmp> pq;
        unordered_map<int,int> mp;

        for(int i=0;i<nums.size();i++)
        {
            mp[nums[i]]++;
        }
        vector<int> m;
        for(const auto& g:mp)
        {
            pq.push({g.first,g.second});
            if(pq.size()>k)
            pq.pop();
        }
        while(!pq.empty())
        {   m.push_back(pq.top().first);
            pq.pop();
        
        }
        return m;
    }
};



//T.C =O(nlogn)
// class Solution {
// public:
// struct cmp{
//     bool operator()(const pair<int,int>& x, pair<int,int>& y ){
//         return x.second<y.second; //Max heap
//     }
// };
//     vector<int> topKFrequent(vector<int>& nums, int k) {
//         priority_queue<pair<int,int>,vector<pair<int,int>>,cmp> pq;
//         unordered_map<int,int> mp;

//         for(int i=0;i<nums.size();i++)
//         {
//             mp[nums[i]]++;
//         }
//         vector<int> m;
//         for(const auto& g:mp)
//         {
//             pq.push({g.first,g.second});
//         }
//         while(k>0)
//         {   m.push_back(pq.top().first);
//             pq.pop();
//             k--;
//         }
// return m;
//     }
// };
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