AddBinary.java

public class AddBinary {
    /**
     * 二进制相加
     */
    public static String addBinary(String a, String b) {
        StringBuilder sb = new StringBuilder();
        int i = a.length() - 1, j = b.length() - 1, carry = 0;
        while (i >= 0 || j >= 0) {
            int sum = carry;
            if (j >= 0) sum += b.charAt(j--) - '0';
            if (i >= 0) sum += a.charAt(i--) - '0';
            sb.append(sum % 2);
            carry = sum / 2;
        }
        if (carry != 0) sb.append(carry);
        return sb.reverse().toString();
    }

    public static void main(String[] args) {
        // 17 -> 1
        // 9 -> 1
        //4 -> 0
        // 2 -> 0
        // 1 -> 0
        // 0 -> 1
        // 1 + 16
        System.out.println(addBinary("11", "1")); // 12 + 5 = 17
    }
}