Q67 Add Binary

Given two binary strings, return their sum (also a binary string).

For example,
a = "11"
b = "1"
Return "100".

解题思路：

使用Python的内置函数 .zfill(总长度) 将 a、b两字符串补为相等的字符串，然后从后往前相加。

Python实现：

class Solution:
    def addBinary(self, a, b):
        """
        :type a: str
        :type b: str
        :rtype: str
        """
        ans = ''
        alen = len(a); blen = len(b)
        if alen < blen:  # 如果两字符串不相等，则较短的字符串前面补0到与较长的字符串等长
            a = a.zfill(blen)
        elif alen > blen:
            b = b.zfill(alen)
        bit = 0
        i = len(a) - 1
        while i >= 0:
            if int(a[i]) + int(b[i]) + bit == 0:
                ans = '0' + ans
                bit = 0
            elif int(a[i]) + int(b[i]) + bit == 1:  
                ans = '1' + ans
                bit = 0
            elif int(a[i]) + int(b[i]) + bit == 2: #产生进位
                ans = '0' + ans
                bit = 1
            else:  #产生进位
                ans = '1' + ans
                bit = 1
            i -= 1
        if bit == 1: # 如果最后还有进位
            ans = '1' + ans
        return ans

a = "11"
b = "111"
c = Solution()
print(c.addBinary(a,b)) # '1010'