LeetCode Top K Frequent Elements

Description

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].
Note:

  • You may assume k is always valid, 1 ≤ k ≤ number of unique elements.
  • Your algorithm’s time complexity must be better than O(n log n), where n is the array’s size.

The original problem is here.

My Solution

I solve this problem in C++, as below:

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class Solution {
public:
    vector<int> topKFrequent(vector<int>& nums, int k) {
        map<int, int> freq;
        for (int i = 0; i < nums.size(); i++) {
            freq[nums[i]] ++;
        }
        priority_queue<pair<int,int>> vecFreq;
        for(map<int,int>::iterator iter=freq.begin(); iter != freq.end(); iter++) {
            vecFreq.push(make_pair(iter->second,iter->first));
        }
        vector<int> res;
        for(int i=0;i<k;i++) {
            res.push_back(vecFreq.top().second);
            vecFreq.pop();
        }
        return res;
    }
};

Note

To solve the problem, use maxHeap, namely priority_queue in C++.