class Solution:    # @param a, a string    # @param b, a string    # @return a string    def addBinary(self, a, b):        #长度不等，补齐        len_a=len(a)        len_b=len(b)        if len_a>len_b:            for i in range(len_a-len_b):                b=‘0‘+b            len_b=len_a        else:            for i in range(len_b-len_a):                a=‘0‘+a            len_a=len_b        res=""        carry=‘0‘        for i in range(len_a):            sum=self.addsingleBinary(a[len_a-i-1],b[len_b-i-1],carry)            if sum==‘3‘:                res=‘1‘+res                carry=‘1‘                continue            if sum==‘2‘:                res=‘0‘+res                carry=‘1‘                continue            else:                res=sum+res                carry=‘0‘                continue        if carry==‘1‘:            res=‘1‘+res        return res    #单个二进制数以及前一位之和的进数相加    def addsingleBinary(self,x,y,carry):        if carry==‘1‘:            if x==‘1‘ and y==‘1‘:                return ‘3‘            if x==‘0‘ and y==‘0‘:                return ‘1‘            else:                return ‘2‘        if carry==‘0‘:            if x==‘1‘ and y==‘1‘:                return ‘2‘            if x==‘0‘ and y==‘0‘:                return ‘0‘            else:                return ‘1‘if __name__ == ‘__main__‘:    s=Solution()    print(s.addBinary("111","110"))