The challenge
Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
Note: For the purpose of this problem, we define empty string as valid palindrome.
Example 1:
Input: "A man, a plan, a canal: Panama" Output: true
Example 2:
Input: "race a car" Output: false
Constraints:
s
consists only of printable ASCII characters.
The solution in Java
class Solution { // take in a String public boolean isPalindrome(String s) { // remove all non-alphanumeric characters and lowercase everything s = s.replaceAll("\\P{Alnum}", "").toLowerCase(); // loop through the String for (int i=0; i<s.length(); i++) { // if the beginning and last characters don't match, return false // also walk in both directions and do the same if (s.charAt(i)!=s.charAt(s.length()-i-1)) return false; } // return true if we get here return true; } }