字符串---Add Binary

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

public class Solution {    /**     * @param a a number     * @param b a number     * @return the result     */    public String addBinary(String a, String b) {        int carry = 0;        String res = "";        int i = 0;        int aLen = a.length();        int bLen = b.length();        while(i < aLen || i < bLen || carry != 0) {            int x = 0;            int y = 0;            if(i < aLen && a.charAt(aLen - 1 -i) == '1')                x = 1;            if(i < bLen && b.charAt(bLen - 1 -i) == '1')                y = 1;            res = (x+y+carry) % 2 + res;            carry = (x+y+carry) / 2;            i++;        }    return res;    }}