[E].[Py].2441.LargestPositiveIntegerThatExistsWithItsNegative

class Solution(object):
    def findMaxK(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        """new_list = [x for x in nums if -x in nums]
        if len(new_list) == 0:
            return -1
        return max(new_list)"""
        checked = {}
        max_num = -1
        for num in nums:
            if num not in checked and (-num) not in checked:
                checked[num] = True
            else:
                if (-num) not in checked:
                    continue
                if abs(num) > max_num:
                    max_num = abs(num)
        return max_num