leetcode-137题:single numberii

class Solution(object):
    def singleNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        ones = [0]*32
        negative = 0
        for n in nums:
            if bin(n)[0] == '-':
                n = bin(n)[3:]
                negative = (negative+1)%3
            else:
                n = bin(n)[2:]
            for i in range(0,len(n)):
                if n[i] == '1':
                    ones[32-(len(n)-i)] = (ones[32-(len(n)-i)] + 1)%3
        res = int(''.join([str(one) for one in ones]),2)
        if negative == 1:
            res = -res
        return res