[LeetCode] Add Binary

"11"

"1"

"100"

class Solution {
public:
string addBinary(string a, string b) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
int lengtha=a.length();
int lengthb=b.length();
int maxlength=lengtha;
if(lengthb > maxlength)
maxlength=lengthb;

int num1,num2,sum;
int carry=0;
string result="";
for(int i=maxlength-1;i>=0;i--)
{
if( lengtha-(maxlength-i) >= 0)
{
num1=a[lengtha-(maxlength-i)]-'0';
}
else{
num1=0;
}
if( lengthb-(maxlength-i) >= 0)
{
num2=b[lengthb-(maxlength-i)]-'0';
}
else{
num2=0;
}
sum=num1+num2+carry;
if(sum>=2)
{
sum=sum-2;
carry=1;
}
else{
carry=0;
}
char tmp='0'+sum;
result=tmp+result;
}
if(carry==1)
{
char tmp='0'+carry;
result=tmp+result;
}

return result;
}
};