67. Add Binary java solutions

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) {
        
        if(a.length() > b.length()){//将字符串长的作为b，方便后面字符串长的处理
            String tmp = b;
            b = a;
            a = tmp;
        }
        int alen = a.length()-1, blen = b.length()-1;
        String ans = "";
        int high = 0, tmp = 0;
        while(alen >= 0){
            tmp = (int)(a.charAt(alen--)-'0') + (int)(b.charAt(blen--)-'0') + high;// 需要做下int的强制类型转换，不然internal error
            ans = "" + tmp%2 + ans;
            high = tmp/2;
        }
        while(blen >= 0){
            tmp = (int)(b.charAt(blen--)-'0') + high;
            ans = "" + tmp%2 + ans;
            high = tmp/2;
        }
        if(high == 1) ans ="" + 1 + ans;
        return ans;
    }
}