algorithm notes: leetcode#414 third maximum number

class :
    def thirdMax(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        maxNums = [float('-Inf')] * 3
        for num in nums:
            if num not in maxNums:
                if num > maxNums[0]:
                    maxNums = [num, maxNums[0], maxNums[1]]
                elif num > maxNums[1]:
                    maxNums = [maxNums[0], num, maxNums[1]]
                elif num > maxNums[2]:
                    maxNums[2] = num
        return maxNums[-1] if float('-Inf') not in maxNums else maxNums[0]