Question

Implement the static method declared as follows:

/** * Divides {@code n} by 2. * * @param n *            {@code NaturalNumber} to be divided * @updates n * @ensures 2 * n <= #n < 2 * (n + 1) */ private static void divideBy2(NaturalNumber n) {...}

()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()()

Implement the static method declared as follows:

/** * Checks whether a {@code String} is a palindrome. * * @param s *            {@code String} to be checked * @return true if {@code s} is a palindrome, false otherwise * @ensures isPalindrome = (s = rev(s)) */ private static boolean isPalindrome(String s) {...}

Recursion needs to be used for both of these, and the NaturalNumber class needs to be used for the top method.

Answer 1

/**
 * Checks whether a {@code String} is a palindrome.
 *
 * @param s
 *            {@code String} to be checked
 * @return true if {@code s} is a palindrome, false otherwise
 * @ensures isPalindrome = (s = rev(s))
 */
private static boolean isPalindrome(String s) {
    if(s.length() <= 1) {
        return true;
    } else {
        if(s.charAt(0) != s.charAt(s.length()-1)) {
            return false;
        } else {
            return isPalindrome(s.substring(1, s.length()-1));
        }
    }
}

/** * Checks whether a {@code String} is a palindrome. * * @param s * {@code String} to be checked * @return true if {@code s} is a palindrome, false otherwise * @ensures isPalindrome = (s = rev(s)) */ private static boolean isPalindrome(String s) { if(s.length() < = 1) { return true: } else { if(s.charAt(0) != s.charAt(s.length()-1)) { return false: } else { return isPalindrome(s.substring(1, s.length()-1)): } } }