Add Binary

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

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

博主对于自己那冗长的代码真是累感不爱了～连注释都不用标了，特别清晰明了，捂脸逃走～只能安慰自己起码跑过了。。。

public class Solution {
    public String addBinary(String a, String b) {
  String n1=new StringBuilder(a).reverse().toString();
         String n2=new StringBuilder(b).reverse().toString();
         StringBuilder sb= new StringBuilder();
         int l=Math.min(a.length(),b.length());
         int carry=0;
         int digit=0;
         for(int i=0;i<l;i++){
             digit=carry+n1.charAt(i)-'0'+n2.charAt(i)-'0';
             if(digit==2){
                 digit=0;
                 carry=1;
             } else if(digit==3){
                 digit=1;
                 carry=1;
             }else{
                 carry=0;
             }
             sb.insert(0,digit);
         }        
        if(a.length()>b.length()){
           for(int i=l;i<a.length();i++){
                digit=carry+n1.charAt(i)-'0';
                 if(digit==2){
                     digit=0;
                     carry=1;
                 }else{
                     carry=0;
                 }
                 sb.insert(0,digit); 
            }
        }
        if(a.length()<b.length()){
               for(int i=l;i<b.length();i++){
                    digit=carry+n2.charAt(i)-'0';
                     if(digit==2){
                         digit=0;
                         carry=1;
                     }else{
                         carry=0;
                     }
                     sb.insert(0,digit); 
                }
            }
        if(carry==1){
            sb.insert(0,carry);
        } 
        return sb.toString(); 
    }
}