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:
sconsists 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;
}
}