Leet Code: Problem # 347 - Top K Frequent Elements

Problem Statement:

Give an array of integers return the k most frequent elements.

Example 1:

Input:

[10, 10, 10, 20, 20, 20, 20, 30, 30]

k = 2

Output:

[20, 10]

Example 2:

Input:

[10, 10, 30]

k = 1

Output:

[10]

Solution in C++:

class Solution {

public:

    vector<int> topKFrequent(vector<int>& nums, int k) {

        unordered_map<int, int> freq;        

        for(int iter = 0; iter < nums.size(); ++iter){

            ++freq[nums[iter]];

        }  

        priority_queue<pair<int, int>> pq;

        for(auto iter = freq.begin(); iter != freq.end(); ++iter){

            pq.push(pair<int, int>(iter->second, iter->first));

        }

        vector<int> res;

        int i = 0;

        while(i++ < k){

            auto val = pq.top();

            res.push_back(val.second);

            pq.pop();

        }

        return res;

    }

};