public class Recursion {
	public static void main(String[] args) {
		System.out.println(pow(2, 6));

		printBinary(6);

		System.out.println(isPalindrome("madam")); // true
		System.out.println(isPalindrome("palindrome")); // false
		System.out.println(isPalindrome("racecar")); // true
		System.out.println(isPalindrome("step on no pets")); // true
		System.out.println(isPalindrome("able was I ere I saw elba")); // true
		System.out.println(isPalindrome("Java")); // false
		System.out.println(isPalindrome("rotater")); // false
		System.out.println(isPalindrome("byebye")); // false
		System.out.println(isPalindrome("notion")); // false
	}

	// Returns the result of raising the base to the specified exponent.
	// pre: exp >= 0
	public static int pow(int base, int exp) {
		if (exp == 0) {
			return 1;
		} else if (exp % 2 == 0) {
			// 2^16 --> (2^2)^8
			// base^exp -> (base^2)^exp/2
			return pow(base * base, exp / 2);
		} else {
			// 2^0 = 1
			// 2^1 = 1 * 2
			// 2^2 = 1 * 2 * 2
			// 2^3 = 1 * 2 * 2 * 2
			return base * pow(base, exp - 1);
		}
	}

	// Prints the given decimal value in binary
	// pre: decimal >= 0
	public static void printBinary(int decimal) {
		if (decimal < 2) {
			System.out.print(decimal);
		} else {
			printBinary(decimal / 2);
			printBinary(decimal % 2);
			// last digit by doing mod 2 and CONVERT IT TO BINARY
			// get the rest by doing / 2 and CONVERT IT TO BINARY
		}
	}

	// Returns true if the given String reads the same
	// forwards as backwards and false otherwise.
	public static boolean isPalindrome(String word) {
		if (word.length() < 2) {
			return true;
		} else {
			// a word is a palindrome if the first and last characters match
			// and the rest is a palindrome

			// char first = word.charAt(0);
			// char last = word.charAt(word.length() - 1);
			//
			// if (first != last) {
			// return false;
			// }
			// // the first and last match so see if the rest is a palindrome
			// return isPalindrome(word.substring(1, word.length() - 1));

			// "zen" version
			return word.charAt(0) == word.charAt(word.length() - 1)
					&& isPalindrome(word.substring(1, word.length() - 1));
		}
	}
}