题目：

题解：

class Solution:
    def thirdMax(self, nums: List[int]) -> int:
        a, b, c = None, None, None
        for num in nums:
            if a is None or num > a:
                a, b, c = num, a, b
            elif a > num and (b is None or num > b):
                b, c = num, b
            elif b is not None and b > num and (c is None or num > c):
                c = num
        return a if c is None else c