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Reverse a string with recursion and iteration

7 replies on 1 page. Most recent reply: Apr 20, 2003 6:36 PM by Kishori Sharan

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Natalie

Posts: 1
Nickname: nat05
Registered: Mar, 2003

Reverse a string with recursion and iteration

Posted: Mar 17, 2003 4:50 AM

Reply

Advertisement

Hi there,

I havent been doing java 4 long and am struggeling trying to write 2 methods:

1) which reverses a string using recursion
2) which reverses a string using iteration

I would be greatful for any help! Thanx xxxx

Rich Burgis

Posts: 17
Nickname: songbird
Registered: Mar, 2003

Re: Reverse a string with recursion and iteration

Posted: Mar 17, 2003 6:40 PM

Reply

Try the following pseudo code

String reverse( String _s )
if length of _s == 0
return "";
else
return reverse( _s.substring( 1 ) ) + _s.charAt( 0 );

The iteration version is similar

Good luck
Rich

> Hi there,
>
> I havent been doing java 4 long and am struggeling trying
> to write 2 methods:
>
> 1) which reverses a string using recursion
> 2) which reverses a string using iteration
>
> I would be greatful for any help! Thanx xxxx

hien

Posts: 2
Nickname: hien
Registered: Apr, 2003

Re: Reverse a string with recursion and iteration

Posted: Apr 17, 2003 2:11 PM

Reply

how do you reverse a string without using the substring predefined method... ???

hien

hien

Posts: 2
Nickname: hien
Registered: Apr, 2003

Re: Reverse a string with recursion and iteration

Posted: Apr 17, 2003 2:37 PM

Reply

I have a class RString. I can't use the predefined methods except for charAt(),concatenation(+) and length(). I need to reverse a string, get the position of a particular character, check the two RStrings for equality(equals method(if teh same exact characters are in the same order adn return true if the Rstrings are identical, false otherwise. I also need to check to see if the string is a palindrome and be able to remove a character in the string. all this is in recursion. I only have so far iterations and kinda hard to do recursion. PLease help!

so my methods will be constructor: public RString(String s)
value = s;

public String toString()
return value;

public in indedOf(char c)

public boolean equals(RString other)

public removeAll(char c)

public reverse()

public boolean isPalindrome(String s)

Arun

Posts: 2
Nickname: lion
Registered: Apr, 2003

Re: Reverse a string with recursion and iteration

Posted: Apr 18, 2003 10:05 AM

Reply

Here's a program which does it:

public String reverseString(String str)
{
char a=str.charAt( str.lastIndexOf(str) );
char[] ch=str.toCharArray();
char[] rev=new char[ ch.length];
for( int i=ch.length-1;i>=0;--i)
{
rev[(ch.length-1)-(i)] =ch;
}
return String.valueOf(rev);
}

Arun

Posts: 2
Nickname: lion
Registered: Apr, 2003

Re: Reverse a string with recursion and iteration

Posted: Apr 18, 2003 11:47 AM

Reply

This seems to be a school assignment going by the restrictions placed.
Here is one primitive program which does your work thru recursion without using substring().
Take this as a template and modify it:

public String reverseString(String str)
{
if (str.equals(""))
return "";
else
{
char ch=str.charAt(0);
String substr= buildString(str);
//System.out.println(substr);
return reverseString(substr) +ch ;
}

}

public String buildString( String str)
{

char[] st=new char[str.length()];
for(int i=1;i<str.length();++i)
{
st=str.charAt(i);
}
return new String(st).trim();

}

FYI there is a very very easy way to reverse a string: using StringBuffer so you don't have to do all this circus

-Arun

Johnny Doe

Posts: 1
Nickname: panther
Registered: Apr, 2003

Re: Reverse a string with recursion and iteration

Posted: Apr 19, 2003 10:28 PM

Reply

With the question that was asked before about the RString program. I believe this person is looking for a way to do this entire program without using the built in substring fucntion plus the .equals fucntion to compare strings. I know this, because I am also looking for the solution to this. How do we step through the characters in the string without using any for loops? For loops are restricted from us in this program also. Thanks for all your help.

Kishori Sharan

Posts: 211
Nickname: kishori
Registered: Feb, 2002

Here is reverse string by recursion...

Posted: Apr 20, 2003 6:36 PM

Reply

Here is reverse string by recursion... It uses only charAt(), length() and + cancatenation ....

 
public class Test {
 
	public static void main (String[] args) throws Exception {
 
		String str = "abc";
		System.out.println ( str + ":" + reverseString ( str ) ) ;
 
		str = "Hello";
		System.out.println ( str + ":" + reverseString ( str ) ) ;
 
		str = "noon";
		System.out.println ( str + ":" + reverseString ( str ) ) ;
 
		str = "This is a bog string";
		System.out.println ( str + ":" + reverseString ( str ) ) ;
 
		str = "recursion";
		System.out.println ( str + ":" + reverseString ( str ) ) ;
 
 
 
	}
 
 
	public static String reverseString ( String source ) {
		if ( source == null ) {
			return null;
		}
 
		int len = source.length() ;
 
		if ( len == 0 || len == 1 ) {
			return source;
		}
 
		return reverseString ( source, source.length()) ;
	}
 
	public static String reverseString (String source, int position ) {
		if ( position <= 0 ) {
			return "";
		}
		else {
			String newStr = source.charAt( position - 1 ) + reverseString (source, --position);
			return newStr;
		}
 
	}
 
}

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