字符串系列一＞二进制求和

class Solution {
    public String addBinary(String a, String b) {
        StringBuffer ret = new StringBuffer();
        int t = 0;
        char[] aa = a.toCharArray();
        char[] bb = b.toCharArray();
        int cur1 = aa.length-1, cur2 = bb.length-1;
        
        while(cur1 >= 0 || cur2 >= 0 || t != 0){

            if(cur1 >= 0) t += aa[cur1--] - '0';
            if(cur2 >= 0) t += bb[cur2--] - '0';
            ret.append((char)((char)(t % 2) + '0'));
            t /= 2;
        }
        ret.reverse();
        return ret.toString();
    }
}