/** Recursion.java -- Let's write some recursive functions.  Practically
 *  anything you can do with a loop, you can also do recursively.
 */
import java.util.Scanner;
import java.util.StringTokenizer;

public class Recursion
{
  private static int [] a = { 7, 2, 9, 4, 1, 6 };

  public static void main(String [] args)
  {
    // simple I/O examples
    System.out.println("List of numbers:  " + count(10));
    System.out.println("The sum 1..10 equals " + sum(10));  
    System.out.println("Star pattern:\n" + triangle(5));

    // practice with strings
    Scanner kbd = new Scanner(System.in);
    System.out.print("\nEnter a string:  ");
    String s = kbd.nextLine();
    System.out.println("Reversal is:  " + reverse(s));
    System.out.println("palindrome() returns " + palindrome(s));

    // practice with a string tokenizer
    System.out.print("\nEnter a list of numbers:  ");
    s = kbd.nextLine();
    StringTokenizer tok = new StringTokenizer(s, ", ");
    System.out.println("sum is " + sumToken(tok));

    // practice with arrays
    System.out.println("\nLargest element of array is " + max(a, 0));
    System.out.println("Array sum is " + sumArray(a, 0));

    // to/from binary
    System.out.print("\nEnter a positive integer:  ");
    int n = Integer.parseInt(kbd.nextLine());
    s = toBinary(n);
    System.out.println("Binary equivalent is " + s);
    n = toInt(s);
    System.out.println("Converting back to integer:  " + n);
  }

  public static String count(int n)
  {




  }

  public static int sum(int n)
  {




  }

  // Print a row (horizontal line) of stars.
  public static String starLine(int n)
  {




  }

  // Make a right triangle filled with stars.  Makes use of starLine()
  // above to simulate a nested loop.
  // In the recursive case, we make sure to print the first n-1 rows, then
  // append the current row of stars, and then a newline.
  public static String triangle(int n)
  {




  }

  public static String reverse(String s)
  {




  }

  public static boolean palindrome(String s)
  {








  }

  // Recursion can also replace a "while" loop.
  // Here we find the sum of numbers that are tokens in a string.
  public static int sumToken(StringTokenizer tok)
  {




  }

  // Find the largest element of (at least part of) an array.
  // We take 2 parameters - the array and the starting index.
  public static int max(int [] a, int start)
  {











  }

  // Find the sum of the elements in an array.  Analogous to finding the max.
  public static int sumArray(int [] a, int start)
  {




  }

  // Convert a positive integer value to a binary string.
  public static String toBinary(int n)
  {






  }

  // Convert an unsigned binary string to an integer.
  public static int toInt(String s)
  {






  }
}