leetcode-67. Add Binary

题目：

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

For example,
a = “11”
b = “1”
Return “100”.

public class Solution {    public String addBinary(String a, String b) {        String sb = "";        int i = a.length()-1, j = b.length()-1,c = 0;        for(;i >= 0 && j >= 0 ; i--,j--){            int n1 = a.charAt(i)-'0';            int n2 = b.charAt(j)-'0';            n1 = n1+n2+c;            c = n1/2;            n1 = n1%2;            sb = n1+sb;        }        System.out.println(i+" "+c+" "+j);        while(i>=0){            int n1 = a.charAt(i)-'0';            n1 = n1 + c;            c = n1/2;            n1 = n1%2;            sb = n1+sb;            i--;        }        while(j>=0){            int n1 = b.charAt(j)-'0';            n1 = n1 + c;            c = n1/2;            n1 = n1%2;            sb = n1+sb;            j--;        }        if(c==1) sb = 1+sb;        return sb.length()==0?"0":sb;    }}