palindrome

This question is an educational demonstration of the usage of lookahead, nested reference, and conditionals in a PCRE pattern to match ALL palindromes, including the ones that can't be matched by the recursive pattern given in the PCRE man page. Examine this PCRE pattern in PHP snippet: $palindrome = '/(?x) ^ (?: (.) (?= .* ( \1 (?(2) \2 | ) ) $ ) )* .? \2? $ /'; This pattern seems to detect palindromes, as seen in this test cases ( see also on ideone.com ): $tests = array( # palindromes '', 'a', 'aa', 'aaa', 'aba', 'aaaa', 'abba', 'aaaaa', 'abcba', 'ababa', # non-palindromes 'aab', 'abab',

I need help writing a recursive function which detects whether a string is a palindrome. But i can't use any loops it must be recursive. Can anyone help show me how this is done. I need to learn this for an upcoming midterm. Im using Python. def ispalindrome(word): if len(word) < 2: return True if word[0] != word[-1]: return False return ispalindrome(word[1:-1]) And here is the best one liner def ispalindrome(word): return word == word[::-1] From a general algorithm perspective, the recursive function has 3 cases: 1) 0 items left . Item is a palindrome , by identity. 2) 1 item left . Item is a

I have a string as input and have to break the string in two substrings. If the left substring equals the right substring then do some logic. How can I do this? Sample: public bool getStatus(string myString) { } Example: myString = "ankYkna" , so if we break it into two substring it would be: left-part = "ank" , right-part = "ank" (after reversal). ionden public static bool getStatus(string myString) { string first = myString.Substring(0, myString.Length / 2); char[] arr = myString.ToCharArray(); Array.Reverse(arr); string temp = new string(arr); string second = temp.Substring(0, temp.Length /

Can I get a recursive Prolog predicate having two arguments, called reverse, which returns the inverse of a list: Sample query and expected result: ?- reverse([a,b,c], L). L = [c,b,a]. A recursive Prolog predicate of two arguments called palindrome which returns true if the given list is palindrome. Sample query with expected result: ?- palindrome([a,b,c]). false. ?- palindrome([b,a,c,a,b]). true. Ad 1: It is impossible to define reverse/2 as a ( directly edit thx to @repeat: tail) recursive predicate - unless you permit an auxiliary predicate. Ad 2: palindrome(X) :- reverse(X,X). But the

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){ System.out.println(isPalindrome("noon")); System.out.println(isPalindrome("Madam I'm Adam")); System.out.println(isPalindrome("A man, a plan, a canal, Panama")); System.out.println(isPalindrome("A Toyota")); System.out.println(isPalindrome("Not a Palindrome")); System.out.println(isPalindrome("asdfghfdsa")); } public static boolean isPalindrome(String in){ if(in.equals(" ") || in.length() == 1 ) return true; in= in.toUpperCase(); if

This is the third part in a series of educational regex articles. It follows How does this regex find triangular numbers? (where nested references is first introduced) and How can we match a^n b^n with Java regex? (where the lookahead "counting" mechanism is further elaborated upon). This part introduces a specific form of nested assertion, which when combined with nested references allows Java regex to match what most people believe is "impossible": palindromes!! The language of palindromes is non- regular ; it's actually context-free (for a given alphabet). That said, modern regex

I wonder how to write palindrome in javascript, where I input different words and program shows if word is palindrome or not. For example word noon is palindrome, while bad is not. Thank you in advance. tnanoba function palindrome(str) { var len = str.length; var mid = Math.floor(len/2); for ( var i = 0; i < mid; i++ ) { if (str[i] !== str[len - 1 - i]) { return false; } } return true; } palindrome will return if specified word is palindrome, based on boolean value (true/false) UPDATE: I opened bounty on this question due to performance and I've done research and here are the results: If we