67. Add Binary

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

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

class Solution {
public:
string addBinary(string a, string b) {
int aLen = a.length();
int bLen = b.length();
bool carry = false;
int aPointer = aLen-1;
int bPointer = bLen-1;
if(aLen >= bLen){
while(bPointer >=0)
{
if(!carry){
if(a[aPointer] == '0' && b[bPointer] == '0')
{
a[aPointer] = '0';
}
else if(a[aPointer] == '1' && b[bPointer] == '1')
{
a[aPointer] = '0';
carry = true;
}
else
{
a[aPointer] = '1';
}
}
else
{
if(a[aPointer] == '0' && b[bPointer] == '0')
{
a[aPointer] = '1';
carry = false;
}
else if(a[aPointer] == '1' && b[bPointer] == '1')
{
a[aPointer] = '1';
}
else
{
a[aPointer] = '0';
}
}
aPointer--;
bPointer--;
}
while(aPointer>=0 && carry)
{
if(a[aPointer] == '0')
{
a[aPointer] = '1';
carry = false;
break;
}
a[aPointer]='0';
aPointer--;
}
if(carry)
{
a = "1" + a;
}
return a;
}
else{
while(aPointer >=0)
{
if(!carry){
if(a[aPointer] == '0' && b[bPointer] == '0')
{
b[bPointer] = '0';
}
else if(a[aPointer] == '1' && b[bPointer] == '1')
{
b[bPointer] = '0';
carry = true;
}
else
{
b[bPointer] = '1';
}
}
else
{
if(a[aPointer] == '0' && b[bPointer] == '0')
{
b[bPointer] = '1';
carry = false;
}
else if(a[aPointer] == '1' && b[bPointer] == '1')
{
b[bPointer] = '1';
}
else
{
b[bPointer] = '0';
}
}
aPointer--;
bPointer--;
}
while(bPointer>=0 && carry)
{
if(b[bPointer] == '0')
{
b[bPointer] = '1';
carry = false;
break;
}
b[bPointer] = '0';
bPointer--;
}
if(carry)
{
b = "1" + b;
}
return b;
}
}
};