First Unique Even Element — Python

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

import collections


# freq table
class Solution(object):
    def firstUniqueEven(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        cnt = collections.defaultdict(int)
        for x in nums:
            cnt[x] += 1
        for x in nums:
            if x%2 == 0 and cnt[x] == 1:
                return x
        return -1