LeetCode - 347.Top K Frequent Elements QuestionEditorial Solution My Submissions

347. Top K Frequent Elements  QuestionEditorial Solution  My Submissions
Total Accepted: 28149
Total Submissions: 63972
Difficulty: Medium
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.

    def topKFrequent(self, nums, k):
        """
        All elements in the nums array can be a candidate of the final outputs. We use the dictionary candidates to count the number of appearance of candidates.
        
        
        """
        count_qualified = 0     # number of qualified candidates
                                # the initial value is obviously 0.
        level = 0               # if candidates[n] > level the n is qualified
                    
        candidates = {}
        
        for n in nums:
            candidates[n] = candidates.get(n,0) + 1  # add 1 to the count
            
            if candidates[n] == level + 1:    

                # this is the only case we care. If candidates[n] <= offset, 

                # then n is not qualified and no impact on the count_effect
                # for candidates[n] > offset + 1, it means that n has been 

                # already counted as qualified. So no impact neither
                count_qualified += 1           # add 1 more qualified candidate 
                
                if count_qualified > k:        

                    # if the number of quanlified candidates is greater than 

                    # the target, we will increase the level of qualification 
                    level += 1
                    for item in candidates.values():# update the count_quanlified
                        if item == level:
                            count_qualified -= 1
        
        
        res = [key for key,val in candidates.items() if val > level]
                        
        return res