leetcode-Add Binary

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

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

思路：与处理合并链表类似，两个指针分别遍历，主要是注意处理进位等细节

代码：

 string addBinary(string a, string b) {
        int len1=a.length();
int len2=b.length();


int len=len1>len2?len1:len2;
string res(len+1,'0');
int count=len;


int i=len1-1;
int j=len2-1;
int carry=0;
while(i>=0 && j>=0)
{
if(carry+a[i]-48+b[j]-48 == 3)
{
res[count]='1';
--count;
carry=1;
}
else if(carry+a[i]-48+b[j]-48 == 2)
{
res[count]='0';
--count;
carry=1;
}
else if(carry+a[i]-48+b[j]-48 == 1)
{
res[count]='1';
--count;
carry=0;
}
else
{
res[count]='0';
--count;
carry=0;
}
--i;
--j;
}
if(i < 0)
{
while(j>=0)
{
if(carry+b[j]-48 == 2)
{
res[count]='0';
--count;
carry=1;
}
else if(carry+b[j]-48 == 1)
{
res[count]='1';
--count;
carry=0;
}
else
{
res[count]='0';
--count;
carry=0;
}
--j;
}
}
if(j < 0)
{
while(i>=0)
{
if(carry+a[i]-48 == 2)
{
res[count]='0';
--count;
carry=1;
}
else if(carry+a[i]-48 == 1)
{
res[count]='1';
--count;
carry=0;
}
else
{
res[count]='0';
--count;
carry=0;
}
--i;
}
}
res[0]=carry+48;
if(res[0] == '0')
res=res.substr(1,len+1);
return res;
    }