Leetcode 67

给定两个二进制字符串，返回他们的和（用二进制表示）。

输入为非空字符串且只包含数字 1 和 0。

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
        """
        num_a = num_b = 0
        for i in range(len(a)-1, -1, -1):
            num_a += (2 ** (len(a) -1 - i)) * int(a[i])
        
        for j in range(len(b)-1, -1, -1):
            num_b += (2 ** (len(b) -1 - j)) * int(b[j])
        
        result = num_a + num_b
        result = str(bin(result))
        return result[2:]

方法二：

class Solution(object):
    def addBinary(self, a, b):
        """
        :type a: str
        :type b: str
        :rtype: str
        """
        if len(a) == 0: 
        	return b
        if len(b) == 0: 
        	return a
        if a[-1] == '1' and b[-1] == '1':
            return self.addBinary(self.addBinary(a[0:-1], b[0:-1]), '1') + '0'
        if a[-1] == '0' and b[-1] == '0':
            return self.addBinary(a[0:-1], b[0:-1]) + '0'
        else:
            return self.addBinary(a[0:-1], b[0:-1]) + '1'