From:	Patrick Prosser
Sent:	06 November 2010 22:02
To:	zoe_1811@hotmail.com
Cc:	Patrick Prosser
Subject:	Palindrome, recursively defined in java
Attachments:	Palindrome.java

Zoe
if you have java compile and run the attached, taking a string in the command 
line

Palidrome is defined recursively as follows (i.e. palindrome is defined in 
terms of palindrome :)

  s is s palandrome if 
   -  s is 1 character long or is empty OR
   - first and last character of s are the same AND
     the string s' is a palindrome where s' is the substring of s starting at 
position 1 and ending at position n-1

Since s' is smaller than s, on each recurisve call s gets smaller and the 
function terminates with s being of length 1 or being empty, or the first and 
last characters being different.

I think this is neat. It depends on the language dealing with OR (|| in java) 
correctly, i.e. in evaluating  P || Q, correctly.
If P is true Q is not evaluated and if P is false Q is evaluated. Also AND (&& 
in java) must be evaluated correctly, i.e. P && Q, if P is false Q is not 
evaluated.

This may seem small stuff but it is important to understand as it leads to 
clear thinking!!! :)

I love you

xxx


--
Patrick Prosser                     tel:  +44 141 330 4934
Computing Science               fax: +44 141 330 4913
University of Glasgow           web: http://www.dcs.gla.ac.uk/~pat/
Glasgow G12 8RZ              email: pat@dcs.gla.ac.uk