67. Add Binary

2019-05-18

67. Add Binary

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

The input strings are both non-empty and contains only characters 1 or 0.

Example 1:

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Input: a = "11", b = "1"
Output: "100"

Example 2:

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Input: a = "1010", b = "1011"
Output: "10101"

Code:

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class Solution(object):
    def addBinary(self, a, b):
        """
        :type a: str
        :type b: str
        :rtype: str
        """
        #add two binary from back to front, I think it is very self explained, when 1+1 we need a carry.
        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'
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class Solution(object):
    def addBinary(self, a, b):
        """
        :type a: str
        :type b: str
        :rtype: str
        """
        carry = 0
        result = ''

        a = list(a)
        b = list(b)

        while a or b or carry:
            if a:
                carry += int(a.pop())
            if b:
                carry += int(b.pop())

            result += str(carry %2)
            carry //= 2

        return result[::-1]
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