class Solution:

    def singleNumber(self, nums: List[int]) ->int:
        checked = {}
        for num in nums:
            if num in checked:
                del checked[num]
                continue
            checked[num] = True
        return list(checked.keys())[0]

73cfdae31161835316cd89a74354b90cda279e05
<mask token>

class Solution:
    <mask token>

class Solution:

    def singleNumber(self, nums: List[int]) ->int:
        checked = {}
        for num in nums:
            if num in checked:
                del checked[num]
                continue
            checked[num] = True
        return list(checked.keys())[0]
