[E].[Py].136.SingleNumber

# Naive Approach
class Solution:
    def singleNumber(self, nums: List[int]) -> int:
        dictionary = dict()
        for num in nums:
            if num in dictionary:
                dictionary[num] += 1
            else:
                dictionary[num] = 1
        for key in dictionary:
            if dictionary[key] == 1:
                return key
        return 0