leetcode_question_67 Add Binary

"11"

"1"

"100"

bool isAllZero(string a)
{
for (int i = 0; i < a.length(); ++i) {
if (a[i] != '0')return false;
}
return true;
}
string stringxor(string a, string b) {
string res="";
int al = a.length()-1;
int bl = b.length()-1;
for (;al >=0 && bl >= 0; al--,bl--) {
char tmp = '0' + (a[al]-'0')^(b[bl]-'0');
res = tmp + res;
}
if (al >= 0) res = a.substr(0,al+1) + res;
if (bl >= 0) res = b.substr(0,bl+1) + res;
return res;
}

string stringand(string a, string b) {
string res="";
int al = a.length()-1;
int bl = b.length()-1;
for (;al >=0 && bl >= 0; al--,bl--) {
char tmp = '0' + ((a[al]-'0')&(b[bl]-'0'));
res = tmp + res;
}
return res;
}

string addBinary(string a, string b) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
if (a == "") return b;
if (b == "") return a;

string xorres = "";
string andres = "";
do {
xorres = stringxor(a,b);
andres = stringand(a,b);
andres += '0';
a = xorres;
b = andres;
} while (!isAllZero(b));

int i = 0;
for (; i < a.length(); ++i)
if (a[i] != '0') break;
if (i >= a.length())
a = "0";
else
a = a.substr(i);
return a;

}