347. Top K Frequent Elements

用字典存每一个数字出现的次数，作为value值，然后根据value值进行排序，取前k个

class Solution(object):
    def topKFrequent(self, nums, k):
        """
        :type nums: List[int]
        :type k: int
        :rtype: List[int]
        """
        zd = {}
        for n in nums:
            if n not in zd:
                zd[n] = 1
            else:
                zd[n] += 1
        l = sorted(zd, key=lambda x:zd[x], reverse = True)
        res = []
        for key in l:
            res.append(key)
            k -= 1
            if k == 0:
                break
        return res