$ cat ./coding/67-add-binary.md

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67. Add Binary

class Solution:
    def addBinary(self, a: str, b: str) -> str:
        res = ''
        if len(a) > len(b):
            b = '0'*(len(a) - len(b)) + b
        else:
            a = '0'*(len(b) - len(a)) + a

        n = len(a)
        carry = False

        for i in reversed(range(n)):
            if carry:
                if a[i] == b[i]:
                    res += '1'
                    if a[i] == '0':
                        carry = False
                else:
                    res += '0'
            else:
                if a[i] == b[i]:
                    res += '0'
                    if a[i] == '1':
                        carry = True
                else:
                    res += '1'
        if carry:
            res += '1'

        return res[::-1]

$ ls ./coding/ | grep -v 67-add-binary