*Add Binary

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

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

 

 

 

    public String addBinary(String a, String b) {
        if (a==null ||a.length()==0){
            return b;
        }
        
        if (b==null || b.length()==0){
            return a;
        }
        
       StringBuilder sb=new StringBuilder();
       
        
        int lastA=a.length()-1;
        int lastB=b.length()-1;
        int carry=0;
        
        
        while (lastA>=0 ||lastB>=0 ||carry>0){
            int num1=lastA>=0?a.charAt(lastA--)-'0':0;
            int num2=lastB>=0?b.charAt(lastB--)-'0':0;
            int current=(num1+num2+carry)%2;
            carry=(num1+num2+carry)/2;
            
            sb.insert(0, current);
            
            
        }
        
        return sb.toString();
    }

 

reference: http://rleetcode.blogspot.com/2014/02/add-binary-java.html