Method add

python/0371-sum-of-two-integers.py:3–6

(a, b)

class Solution:
    def getSum(self, a: int, b: int) -> int:
        def add(a, b):
            if not a or not b:
                return a or b
            return add(a ^ b, (a & b) << 1)

        if a * b < 0:  # assume a < 0, b > 0
            if a > 0: