class Main {
  public static void main(String[] args) {
    int power = power(2, 5);

    int sumAll = sumAll(10);
   
    System.out.println(power + " " + sumAll);

    countDown(5);
 
    printUpTo(10);

    boolean pal = palindrome("bob");

    System.out.println(pal);
  }

  public static int power(int x, int y) {
    if (y == 0) {
      return 1;
    }

    return x * power(x, y - 1);
  }

  public static int sumAll(int n) {
    if (n == 0) {
      return 0;
    }

    return n + sumAll(n - 1);
  }

  public static void countDown(int n) {
    if (n <= 0) {
      System.out.println("BOOM!");
      return;
    }

    System.out.println(n);
    countDown(n - 1);
  }

  public static void printUpTo(int n) {
    if (n <= 0) {
      return;
    }

    printUpTo(n - 1);
    System.out.println(n);
  }

  public static boolean palindrome(String s) {
    if (s == null) {
      return false;
    }

    if (s.length() <= 1) {
      return true;
    }

    if (s.charAt(0) != s.charAt(s.length() - 1)) {
      return false;
    }

    return palindrome(s.substring(1, s.length() - 1));
  }
}