20-136. Single Number

题目描述：

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

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

代码实现：

1 class Solution(object):
2     def singleNumber(self, nums):
3         """
4         :type nums: List[int]
5         :rtype: int
6         """
7         return reduce(operator.xor, nums)           # method1
8         # return 2*sum(set(nums))-sum(nums)         # method2
9         # return reduce(lambda x, y: x ^ y, nums)   # method3