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

For example,
a = "11"
b = "1"
Return "100".

题意：二进制加法，最后返回字符串，水题，直接上代码

public String addBinary(String a, String b) {
            StringBuilder result = new StringBuilder();
        char[] as = a.toCharArray();
        char[] bs = b.toCharArray();
        int flag = 0;

        int i = as.length - 1, j = bs.length - 1;

        while (i >= 0 && j >= 0) {
            int c = as[i] + bs[j];
            switch (c) {

            case 96:
                if (flag == 0) {
                    result.append(0);
                } else {
                    result.append(1);
                }
                flag = 0;
                break;

            case 97:
                if (flag == 0) {
                    result.append(1);
                    flag = 0;
                } else {
                    result.append(0);
                    flag = 1;
                }

                break;

            case 98:
                if (flag == 0) {
                    result.append(0);
                    flag = 1;
                } else {
                    result.append(1);
                    flag = 1;
                }

                break;
            }
            i--;
            j--;

        }
        if (i == -1) {
            while (j >= 0) {
                if (flag == 1) {
                    if (bs[j] == '0') {
                        result.append('1');
                        flag = 0;
                    } else {
                        result.append(0);
                        flag = 1;
                    }
                } else {
                    result.append(bs[j]);
                }
                j--;
            }
        }

        if (j == -1) {
            while (i >= 0) {
                if (flag == 1) {
                    if (as[i] == '0') {
                        result.append('1');
                        flag = 0;
                    } else {
                        result.append(0);
                        flag = 1;
                    }
                } else {
                    result.append(as[i]);
                }
                i--;
            }
        }
        if (flag == 1) {
            result.append('1');
        }

        return result.reverse().toString();
    }
}