leetcode-136 - Single Number

動機

XOR!!

Problem

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

You must implement a solution with a linear runtime complexity and use only constant extra space.

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.

Sol

((a xor b) xor b) == a

xor兩次就是不變!!

class Solution:
    def singleNumber(self, nums: List[int]) -> int:
        a = 0
        for i in nums:
            a ^= i
        return a