67. Add Binary【E】【44】【leetcode】

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

For example,
a = "11"
b = "1"
Return "100".

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按位相加，还是有些边界条件需要处理的

class Solution(object):    def addBinary(self, a, b):        la = len(a)        lb = len(b)        if la < lb:            a,b = b,a            la,lb = lb,la        res = [''] * (max(len(a),len(b)) + 1)        prp = 0        for i in xrange(1,lb+1):            ta = int(a[-i])            tb = int(b[-i])            #print ta,tb,prp,            resi = ta + tb + prp            if resi > 1:                resi -= 2                prp = 1            else:                prp = 0            res[-i] = str(resi)            #print res        for i in xrange(lb+1,la+1):            ta = int(a[-i])            resi = ta + prp            if resi > 1:                resi -= 2                prp = 1            else:                prp = 0            res[-i] = str(resi)            #print res        if prp == 1:            res[0] = str(prp)        res = ''.join(res)        return res