【leetcode刷题】20T32-二进制求和

示例 1:
输入: a = "11", b = "1"
输出: "100"

示例 2:
输入: a = "1010", b = "1011"
输出: "10101"

class Solution(object):
    def addBinary(self, a, b):
        """
        :type a: str
        :type b: str
        :rtype: str
        """
        if len(a) < len(b):
            a, b = b, a
        add = 0
        res = ''
        # a + b + 进位
        for i in range(1, len(b) + 1):
            tmp = int(a[-i]) + int(b[-i]) + add
            add = tmp // 2
            tmp %= 2
            res += str(tmp)

        # a + 进位
        for i in range(len(b) + 1, len(a) + 1):
            tmp = int(a[-i]) + add
            add = tmp // 2
            tmp %= 2
            res += str(tmp)

        if add == 1:
            res += '1'
        return res[::-1]