# Single Number
# 
# Given an 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?

class Solution:
    
    # @param numbers, a list of integer
    # @return an integer
    def singleNumber(self, numbers):
        val = 0
        for n in numbers:
            val ^= n
        return val
    