136 Single number

Original Description: 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?

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• 要求： 给一个数组，其中的元素只有一个出现一次，其余均出现两次，找出光棍。

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• 返回： 光棍元素

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• 例子：
  • input: [2,2,1]
  • output: 1

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Solution

光棍的值 = set内元素之和x2 - 数组元素之和

class Solution(object):
    def singleNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        return sum(set(nums))*2-sum(nums)
        # or can use dict to save count