Creating a recursive method for Palindrome

Question

I am trying to create a Palindrome program using recursion within Java but I am stuck, this is what I have so far:

 public static void main (String[] args){
         


        

Answer 1

public class PlaindromeNumbers {

int func1(int n)
{
    if(n==1)
        return 1;

    return n*func1(n-1);
}

static boolean check=false;
int func(int no)
{

    String a=""+no;

    String reverse = new StringBuffer(a).reverse().toString();

    if(a.equals(reverse))
    {

        if(!a.contains("0"))
        {
           System.out.println("hey");
            check=true;
            return Integer.parseInt(a);
        }

    }

      //  else
      //  {
    func(no++);
    if(check==true)
    {
        return 0;
    }
       return 0;   
   }
public static void main(String[] args) {
    // TODO code application logic here
    Scanner in=new Scanner(System.in);
    System.out.println("Enter testcase");
   int testcase=in.nextInt(); 
   while(testcase>0)
   {
     int a=in.nextInt();
     PlaindromeNumbers obj=new PlaindromeNumbers();
       System.out.println(obj.func(a));
       testcase--;
   }
}

}

Answer 2

Here is a recursive method that will ignore specified characters:

public static boolean isPal(String rest, String ignore) {
    int rLen = rest.length();
    if (rLen < 2)
        return true;
    char first = rest.charAt(0)
    char last = rest.charAt(rLen-1);
    boolean skip = ignore.indexOf(first) != -1 || ignore.indexOf(last) != -1;
    return skip || first == last && isPal(rest.substring(1, rLen-1), ignore);
}

Use it like this:

isPal("Madam I'm Adam".toLowerCase(), " ,'");
isPal("A man, a plan, a canal, Panama".toLowerCase(), " ,'");

It does not make sense to include case insensitivity in the recursive method since it only needs to be done once, unless you are not allowed to use the .toLowerCase() method.

Answer 3

public class palin
{ 
    static boolean isPalin(String s, int i, int j)
    {
        boolean b=true;
        if(s.charAt(i)==s.charAt(j))
        {
            if(i<=j)
                isPalin(s,(i+1),(j-1));
        }
        else
        {
            b=false;
        }
        return b;
    }
    public static void main()
    {
        String s1="madam";
        if(isPalin(s1, 0, s1.length()-1)==true)
            System.out.println(s1+" is palindrome");
        else
            System.out.println(s1+" is not palindrome");
    }
}