Most Frequent Even Element — Python

# Time:  O(n)
# Space: O(n)

import collections


# freq table
class Solution(object):
    def mostFrequentEven(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        cnt = collections.Counter(x for x in nums if x%2 == 0)
        return max(cnt.iterkeys(), key=lambda x: (cnt[x], -x)) if cnt else -1