add binary

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

给你两个二进制字符串，将两者相加，返回一个新的二进制字符串。
例如：
a="11";
b="1";
返回"100";

  public class Solution {
      public String addBinary(String a, String b) {
        int aLen = a.length();
        int bLen = b.length();
        String re = "";
        int next = 0;
        while(aLen>0||bLen>0||next>0){
            int aInt = 0;
            if(aLen>0){
                aInt = a.charAt(aLen-1)-'0';
                aLen--;
            }
            int bInt = 0;
            if(bLen>0){
                bInt = b.charAt(bLen-1)-'0';
                bLen--;
            }
            re=new Integer((aInt+bInt+next)%2)+re;
            next = (aInt+bInt+next)/2;
        }
        return re; 
      }
  }

  class Solution {
  public:
      string addBinary(string a, string b) {
          char carryBit = '0';
          int alen = a.size()-1;
          int blen = b.size()-1;
          string sumStr = "";
          while(alen>=0||blen>=0){
              char aChar = alen>=0?a[alen]:'0';
              char bChar = blen>=0?b[blen]:'0';
              int sum=(carryBit-'0')+(aChar-'0')+(bChar-'0');
              carryBit = (char)('0'+sum/2);
              sumStr=((char)('0'+sum%2))+sumStr;
              alen--;
              blen--;
          }
          sumStr=carryBit=='1'?(carryBit+sumStr):sumStr;
          return sumStr;
      }
  };