python XOR运算

136. 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

solution:

def singleNumber(nums):
    res = 0
    for num in nums:
        res ^= num
        print(res)
    return res  

Q: why XOR works?

A:
For anyone who didn’t understood why this works here is an explanation. This XOR operation works because it’s like XORing all the numbers by itself. So if the array is {2,1,4,5,2,4,1} then it will be like we are performing this operation

((2^2)^(1^1)^(4^4)^(5)) => (0^0^0^5) => 5.

Hence picking the odd one out ( 5 in this case).
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