答案

public class Solution {
    public String addBinary(String a, String b) {
        if(a==null||a==""||b==null||b=="")
        {
            return "";
        }
        char []arrayA=a.toCharArray();
        char []arrayB=b.toCharArray();
        char []arrayC=new char[Math.max(arrayA.length,arrayB.length)];
        int i=arrayA.length-1;
        int j=arrayB.length-1;
        int k=arrayC.length-1;
        int carry=0;
        int sum;
        while(k>=0)
        {
            sum=carry;
            if(i>=0){
                sum+=arrayA[i--]-'0';
            }
            if(j>=0){
                sum+=arrayB[j--]-'0';
            }
            if(sum%2==0){
                arrayC[k--]='0';
            }else{
                arrayC[k--]='1';
            }
            carry=sum>>>1;
        }
        return (carry>0?"1":"")+new String(arrayC);
    }
}