python leetcode 136. Single Number

Given a non-empty array of integers, every element appears twice except for one. Find that single one.

找出列表中只出现一次的数。

Note:

Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

Example 1:

Input: [2,2,1]
Output: 1

Example 2:

Input: [4,1,2,1,2]
Output: 4

class Solution:
    def singleNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        """
        方法一：
        return sum(set(nums))*2 - sum(nums)
        """
        ans = 0
        for x in nums:
            ans = ans ^ x
        return ans