Hi math01-ga,
Welcome back! :-)
As usual, I have provided the required Java code below. To compile
and run
this code, you will need the Java2 SDK. You can download the Java SDK
from :
- Download : Java(TM) 2 SDK, Standard Edition, v 1_4_0_03
( http://java.sun.com/j2se/1.4/download.html )
A free Java IDE (if you need one) can be found at :
- The RealJ Java IDE
( http://www.realj.com )
The code provided below has been tested with RealJ and JDK 1.4.
+-----------------------------------------+
Copy the given code into a file called 'Test.java'. The code
contains the following classes:
+ class Test
| |_____main(String args) :This method tests the recursion
methods.
|
+ class Recursion
|----NumberOfDigits(int)
|----SumRange(int,int)
|----Palindrome(String)
|----Countdown(int)
|----Howmany(int[],int)
+-----------------------------------------+
The recursion methods are pretty simple and pretty much self
explanatory. If you have problem following the flow of the program,
just ask me for a clarification and I will help you out.
As for the requirement of atleast one tail recursive function, the
function Countdown() meets your needs. For a definition of the term
"tail recursion", check out:
- NIST: tail recursion
( http://www.nist.gov/dads/HTML/tailrecursn.html )
So, without further delay, here is the code:
+-----------------------------------------+
import java.io.*;
// Test Class: Contains the main method which tests
// the methods of the Recursion class.
public class Test
{
public static void main(String args[]) throws IOException
{
// Setup out keyboard reader
BufferedReader buf =
new BufferedReader(new InputStreamReader(System.in));
// Create Recursion class object
Recursion R = new Recursion();
int choice = 1;
while( choice!=0 )
{
do
{
System.out.print( "\n\n\tRecursion Test Menu"
+ "\n 1. Test Function NumberOfDigits()"
+ "\n 2. Test Function SumRange()"
+ "\n 3. Test Function Palindrome()"
+ "\n 4. Test Function Countdown()"
+ "\n 5. Test Function Howmany()"
+ "\n 0. Exit"
+ "\n\nEnter Your Choice(0-5): ");
choice = Integer.parseInt( buf.readLine() );
}while( choice<0 || choice>5 );
switch(choice)
{
case 1:
System.out.println(" Testing Function NumberOfDigits() :");
System.out.print(" Enter a number: ");
int num = Integer.parseInt( buf.readLine() );
System.out.println(" The number " + num + " has "
+ R.NumberOfDigits(num) + " digits.");
break;
case 2:
System.out.println(" Testing Function SumRange() :");
System.out.print(" Enter a number n: ");
int n = Integer.parseInt( buf.readLine() );
System.out.print(" Enter a number m: ");
int m = Integer.parseInt( buf.readLine() );
System.out.println(" The sum of numbers from "+n
+" to "+m+" is "+R.SumRange(n,m));
break;
case 3:
System.out.println(" Testing Function Palindrome() :");
System.out.print(" Enter a string : ");
String str = buf.readLine();
System.out.println(" The function returned "
+ R.Palindrome(str) + ".");
break;
case 4:
System.out.println(" Testing Function Countdown() :");
System.out.print(" Enter a number: ");
int count = Integer.parseInt( buf.readLine() );
System.out.println(" The output of this function is: ");
R.Countdown(count);
break;
case 5:
System.out.println(" Testing Function Howmany() :");
System.out.print(" Enter the number of array elements: ");
int arrLen = Integer.parseInt( buf.readLine() );
if( arrLen==0)
break;
// Create array and populate it
int[] array = new int[arrLen];
for(int i=0; i<arrLen; i++)
{
System.out.print(" Enter array element "+i);
array[i] = Integer.parseInt( buf.readLine() );
}
System.out.print(" Enter the number to search for: ");
int search = Integer.parseInt( buf.readLine() );
System.out.println(" The number " +search
+ " appears in the array "
+ R.Howmany(array,search)+ " times.");
break;
} // end Switch Case
// Pause after showing function output
if( choice!=0 )
{
System.out.print("\nPress ENTER to continue....");
buf.readLine();
}
}// End While
}
}
// Recursion Class: Contains the 5 recursive methods
class Recursion
{
// NumberofDigits: returns the number of digits in an integer.
// Divides a number by 10 in a recursive loop,
// adding 1 everytime until the number becomes 0.
public int NumberOfDigits(int num)
{
num = num/10;
if( num == 0)
return 1;
return ( 1+NumberOfDigits(num) );
}
//SumRange: takes two arguments n and m and returns the sum
// of all integers from n to m, both inclusive
public int SumRange( int n, int m )
{
// Make sure that n <= m
if( m<n)
{
// Swap values
int temp = m;
m=n;
n=temp;
}
if( n == m)
return n;
return (n + SumRange( n+1,m ));
}
// Palindrome: checks if a given string is a palindrome.
// Compares the first & last characters in a string
// If they are the same, it removes them and calls itself again.
public boolean Palindrome( String str )
{
int strlen = str.length(); // length of the input string
// A string of length 0 or 1 is always a palindrome
if( strlen==0 || strlen == 1 )
return true;
if( str.charAt(0) == str.charAt(strlen-1) )
return ( Palindrome(str.substring(1, strlen-1)) );
return false;
}
// Countdown: takes a number n and prints out the numbers
// in a decreasing order(till 0)
public void Countdown ( int n )
{
System.out.println( n );
if(n==0)
return;
Countdown(n-1);
}
//Howmany: takes two arguments, an array (of integers) & an integer
&
// returns the no. of times the integer occurs in the array.
public int Howmany ( int[] array, int n )
{
if( array.length == 1 )
if( array[0] == n )
return 1;
else
return 0;
// Create new array
int[] newArray = new int[array.length-1];
// Copy Array
for(int i=0; i<newArray.length; i++)
newArray[i] = array[i+1];
// Check if n is in the current element
if( array[0] == n )
return 1+Howmany(newArray,n);
else
return Howmany(newArray,n);
}
}
+-----------------------------------------+
Hope this helps.
If you need any clarifications, just ask!
Regards,
Theta-ga
==========================================
Google Search Terms Used:
"tail recursion" |
