LC268. Missing Number

class Solution:
    def missingNumber(self, nums: List[int]) -> int:
        return functools.reduce(lambda acc, v: acc ^ v, range(0, len(nums) + 1)) ^ functools.reduce(lambda acc, v: acc ^ v, nums)

Complexity

Time: $O(n)$
Space: $O(1)$ — But $O(n)$ since we use functional approach.

Notes

Can also simply do sumA - sumB