0067：二进制求和

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class Solution:
    def addBinary(self, a: str, b: str) -> str:
        res,c = [],0
        for x,y in zip_longest(a[::-1],b[::-1],fillvalue=0):
            c,r = divmod(int(x)+int(y)+c,2)
            res.append(str(r))
        if c:
            res.append('1')
        return ''.join(res[::-1])