C2.java

int C2(String s) {

    s = s.replace(" ", "");
    
    String t = s.replaceAll("[0-9x^&|~()]", "");
    if(!t.isEmpty()) {
        return -1;
    }

    for (int i = 1; i <= 1000; i++) {
        String c = s.replace("x", String.valueOf(i));
        if (eval(c) == 0) {
            return i;
        }
    }

    return -1;
}

int eval(String s) {
    String exp = "";
    String sub = "";
    int level = 0;

    for (char c : s.toCharArray()) {
        if (c == '(') {
            level++;
            if (level > 1) {
                sub += c;
            }
            continue;
        }
        if (c == ')') {
            level--;
            if (level == 0) {
                exp += eval(sub);
                sub = "";
            } else {
                sub += c;
            }
            continue;
        }
        if (level > 0 || !sub.isEmpty()) {
            sub += c;
        } else {
            exp += c;
        }
    }

    return calc(exp);
}

int calc(String exp) {
    String left = "";
    String right = "";
    String op = "";

    for (char d : exp.toCharArray()) {
        if (Character.isDigit(d)) {
            if (op.isEmpty()) {
                left += d;
            } else {
                right += d;
            }
        } else {
            if (op.isEmpty()) {
                op = String.valueOf(d);
                continue;
            } else {
                left = "" + doMath(left, right, op);
                op = "";
                right = "";
            }
        }
    }

    if (!op.isEmpty()) {
        left = "" + doMath(left, right, op);
    }

    return Integer.parseInt(left);
}

int doMath(String left, String right, String op) {
    if (!left.isEmpty() && !right.isEmpty()) {
        // ^,&,|,~
        switch (op) {
            case "^":
                return Integer.parseInt(left) ^ Integer.parseInt(right);
            case "&":
                return Integer.parseInt(left) & Integer.parseInt(right);
            case "|":
                return Integer.parseInt(left) | Integer.parseInt(right);
        }
    }

    else if (left.isEmpty() && !right.isEmpty() && op.equals("~")) {
        return ~Integer.parseInt(right);
    }

    throw new RuntimeException();
}