只出现一次的数字 II leetcode

给定一个非空整数数组，除了某个元素只出现一次以外，其余每个元素均出现了三次。找出那个只出现了一次的元素。

说明：

你的算法应该具有线性时间复杂度。 你可以不使用额外空间来实现吗？

示例 1:

输入: [2,2,3,2]
输出: 3

示例 2:

输入: [0,1,0,1,0,1,99]
输出: 99

 

class Solution(object):
    def singleNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        res = [0 for _ in range(32)]
        for i in range(32):
            for ele in nums:
                if ele & (2 ** i) == pow(2, i):
                    res[i] += 1
        res = [ele % 3 for ele in res]
        result = 0
        if res[-1] == 0:
            for ind, ele in enumerate(res):
                if ele == 1:
                    result |= 2 ** ind
            return result
        else:
            for ind, ele in enumerate(res[:-1]):
                if ele == 0:
                    result |= 2 ** ind
            return -(result + 1)