palindrome

I have a class that checks whether a string is a palindrome or not. I have two questions. 1) Is this the most efficient way to check for palindrome? 2) Can this be implemented recursively? public class Words { public static boolean isPalindrome(String word) { String pal = null; word = word.replace(" ", ""); pal = new StringBuffer(word).reverse().toString(); if (word.compareTo(pal) == 0) { return true; } else { return false; } } } Have a test class to test this... Doubt its needed but here it is anyways if anyone cares to try it out to be able to help me with any of the two questions above...

I am trying to write a predicate palindrome/1 in Prolog that is true if and only if its list input consists of a palindromic list. for example: ?- palindrome([1,2,3,4,5,4,3,2,1]). is true. Any ideas or solutions? A palindrome list is a list which reads the same backwards, so you can reverse the list to check whether it yields the same list: palindrome(L):- reverse(L, L). Looks that everybody is voting for a reverse/2 based solution. I guess you guys have a reverse/2 solution in mind that is O(n) of the given list. Something with an accumulator: reverse(X,Y) :- reverse(X,[],Y). reverse([],X,X).

Given a string, I know how to find the number of palindromic substrings in linear time using Manacher's algorithm. But now I need to find the number of distinct/unique palindromic substrings. Now, this might lead to an O(n + n^2) algorithm - one 'n' for finding all such substrings, and n^2 for comparing each of these substrings with the ones already found, to check if it is unique. I am sure there is an algorithm with better complexity. I was thinking of maybe trying my luck with suffix trees? Is there an algorithm with better time complexity? I would just put substrings you found into the

I've been learning Ruby, so I thought I'd try my hand at some of the project Euler puzzles. Embarrassingly, I only made it to problem 4... Problem 4 goes as follows: A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99. Find the largest palindrome made from the product of two 3-digit numbers. So I figured I would loop down from 999 to 100 in a nested for loop and do a test for the palindrome and then break out of the loops when I found the first one (which should be the largest one): final=nil range = 100...1000

How can you reverse a string of numbers in R? for instance, I have a vector of about 1000 six digit numbers, and I would like to know if they are palindromes. I would like to create a second set which is the exact reverse, so I could do a matchup. It is actually the decimial representation of the number that you are testing to be a palindrome, not the number itself (255 is a palendrome in hex and binary, but not decimal). You can do this fairly simply using pattern matching: > tmp <- c(100001, 123321, 123456) > grepl( '^([0-9])([0-9])([0-9])\\3\\2\\1$', tmp ) [1] TRUE TRUE FALSE > you could