LeetCode67.二进制求和

给定两个二进制字符串，返回他们的和（用二进制表示）。

输入为非空字符串且只包含数字 1 和 0。

示例 1:

输入: a = "11", b = "1"
输出: "100"

示例 2:

输入: a = "1010", b = "1011"
输出: "10101"

class Solution {
    public String addBinary(String a, String b) {
         StringBuilder sb = new StringBuilder();
        
        int i = a.length()-1;
        int j = b.length()-1;
        int remainder = 0;
        while (i>=0 || j>=0) {
            int sum = remainder;
            if (i>=0) sum+=a.charAt(i)-'0';
            if (j>=0) sum+=b.charAt(j)-'0';
            sb.append(sum % 2);
            remainder = sum/2;
            i--;
            j--;
        }
        if (remainder != 0) {
            sb.append(remainder);
        }
        
        return sb.reverse().toString();
    }
}