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].

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 logn), where n is the array's size.

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利用python可以简单实现：

代码如下：

class Solution(object):
    def topKFrequent(self, nums, k):
        """
        :type nums: List[int]
        :type k: int
        :rtype: List[int]
        """
        m1={}
        for temp in nums:
            if temp not in m1.keys():
                m1[temp]=1
            else:
                m1[temp]+=1
        m1=sorted(m1.iteritems(),key=lambda a:a[1],reverse=True)
        result=[]
        count=0
        for temp in m1:
            if count<k:
                result.append(temp[0])
                count+=1
            else:
                break
        return result