Add Binary(bit.iter,recur)

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

The input strings are bothnon-emptyand contains only characters1or 0.

Example 1:

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

Output:
 "100"

Example 2:

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

Output:
 "10101"

分析

2个数组倒着相加，while i>=0 or j>=0:

模仿十进制这里，i%2 和i//2

class Solution(object):
    def addBinary(self, a, b):
        """
        :type a: str
        :type b: str
        :rtype: str
        """
        i = len(a)-1
        j = len(b)-1
        c = 0
        res=''
        while i>=0 or j>=0:            
            if i >=0:
                c += int(a[i])
                i -=1
            if j>=0:
                c+=int(b[j])
                j-=1

            res=str(c%2)+res
            c = c//2
        if c > 0:
            res = str(c)+res
        return res

recursive

class Solution(object):
    def addBinary(self, a, b):
        """
        :type a: str
        :type b: str
        :rtype: str
        """
        if not a:return b
        if not b:return a
        if int(a[-1])+int(b[-1])== 2:
            return self.addBinary(self.addBinary(a[:-1],b[:-1]),'1')+'0'
        elif int(a[-1])+int(b[-1])==1:
            return self.addBinary(a[:-1], b[:-1]) + '1'
        else:
            return self.addBinary(a[:-1], b[:-1]) + '0'