Add Binary

//Given two binary strings, return their sum (also a binary string).
//
//For example,
//a = "11"
//b = "1"
//Return "100".
public class AddBinary {


public static void main(String[] args) {
// TODO Auto-generated method stub


}
public String addBinary(String a, String b) {
//    if(a.length()==0)
//     return b;
//    if(b.length()==0)
//     return a;
   StringBuilder sb=new StringBuilder();
   int count=0;
   int i;
   int j;
   for(i=a.length()-1,j=b.length()-1;i>=0&&j>=0;i--,j--){
    int avalue=a.charAt(i)-'0';
    int bvalue=b.charAt(j)-'0';
    int sum=avalue+bvalue+count;
    sb.append(sum%2+"");
    count=sum/2;
   }
   if(i<0){
    while(j>=0){
    int sum=b.charAt(j)-'0'+count;
    sb.append(sum%2+"");
    count=sum/2;
    j--;
    }
   }else{
    while(i>=0){
    int sum=a.charAt(i)-'0'+count;
    sb.append(sum%2+"");
    count=sum/2;
    i--;
    }
   }
   if(count>0)
    sb.append(count+"");
   return sb.reverse().toString();
}


}