Problem URL: Missing number

We can XOR the same number to even it out, for example 3^3 or 5^5 will always be 0. That means we can XOR every number form 1 to number of element in our input array and then XOR the input numbers with it. That will even our every number except the missing number.

class Solution:
    def missingNumber(self, nums: List[int]) -> int:
        missing = 0
        for i in range(1, len(nums)+1):
            missing ^= i
        for num in nums:
            missing ^= num
        return missing

Time Complexity: O(n)
Space Complexity: O(1)