Chapter 15 # 5 PC for Starting Out With Java 1st Edition 5) Palindrome Detector

Question

Chapter 15 # 5 PC for Starting Out With Java 1st Edition


5) Palindrome Detector

A palindrome is any word phrase, or sentence that reads the same forward
and backward. Here are some well-known palindromes:
Albe was I, ere I saw Elba
A man, a plan, a canal, Panama
Desserts, I stressed
Kayak

Write a boolean method that uses recursion to determine if a string argument
is a palindrome. The method should return true if the argument reads the same
forward & backward. Demonstrate the method in a program.

Explanation / Answer

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import java.util.*;
public class recursivepalindrone
{
public static void main(String args[])

{
Scanner in =new Scanner(System.in);
boolean palin;
String input;
System.out.print("Enter a string: ");
input=in.nextLine();
palin=isPalindrome(input,0,input.length()-1);
if(palin)
   System.out.println(input+" is a Palindrome");
else
    System.out.println(input+" is not a Palindrome");

}
public static boolean isPalindrome(String str,int low, int high)
{
if(high <= low)
    return true;
if(Character.isDigit(str.charAt (low))||(Character.isLetter(str.charAt (low)))
&&(Character.isDigit((str.charAt (high)))||(Character.isLetter(Character.toUpperCase(str.charAt (high))))))
   if( Character.toUpperCase(str.charAt (low))==Character.toUpperCase(str.charAt (high)))
           return isPalindrome(str,low+1,high-1);
   else     return false;
else
   {
    if(Character.isDigit(Character.toUpperCase(str.charAt (low)))||(Character.isLetter(Character.toUpperCase(str.charAt (low)))))
        return isPalindrome(str,low,high-1);
   else
        return isPalindrome(str,low+1,high);
        }


}
}

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