10. Single Number (#136) [EASY]

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

Follow up: Could you implement a solution with a linear runtime complexity and without using extra memory?

Example 1:

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

Example 2:

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

Example 3:

Input: nums = [1]
Output: 1

Constraints:

• 1 <= nums.length <= 3 * 104
• -3 * 104 <= nums[i] <= 3 * 104
• Each element in the array appears twice except for one element which appears only once.

My solution: O(n)

class Solution:
    def singleNumber(self, nums: List[int]) -> int:
        return sum(set(nums)) * 2 - sum(nums)

Another one using ^=

ret = nums[0]
        for num in nums[1:]:
            ret ^= num
        return ret