public String addBinary(String a, String b) {
String result = "";
int aLen = a.length() - 1;
int bLen = b.length() - 1;
int sum = 0;
while(aLen>=0 || bLen>=0){
if(aLen>=0){
sum +=Integer.parseInt(a.substring(aLen,aLen+1));
aLen--;
}
if(bLen>=0){
sum +=Integer.parseInt(b.substring(bLen,bLen+1));
bLen--;
}
if(sum==2){
result = "0" + result;
sum=1;
}else if(sum==0 || sum==1) {
result = sum +"" + result;
sum = 0;
}else if(sum==3){
result = "1" + result;
sum = 1;
}
}
if(sum==1)
result = "1" + result;
return result;
}