Question

I’m writing a program that determines if a string is a palindrome recursively. I’ve decided to try and use regex, but I’m having a bit of trouble understanding the syntax. What I need to do is compare the first and last char to see if they are identical. How can I go about doing this?

Thanks!

EDIT: I found this helpful: AirSource Ltd’s answer to Degvik’s question

Answer 1

Yes, you can determine using regex if the first and last characters are the same:

str.matches("(.).*\\1")

This uses a “back reference” to refer to “group 1”, which captures the first character.

Example:

"aba".matches("(.).*\\1") // true
"abc".matches("(.).*\\1") // false

You could then recursively remove the first and last characters and check again:

public static boolean isPalindrome(String str) {
    return str.length() < 2 || 
        (str.matches("(.).*\\1") && isPalindrome(str.substring(1, str.length() - 1)));
}