Leetcode 136. Single Number

异或运算的性质:

1. 0^a=a
2. a^a=0
3. a^b^a=a^a^b=0^b=b

所以只需要把全体数字异或运算一遍即可.

class Solution(object):
    def singleNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        ans=nums[0]
        for a in nums[1:]:
            ans^=a
        return ans