125. Valid Palindrome

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.

# @param {String} s
# @return {Boolean}
def is_palindrome(s)
  s = s.downcase.delete("^/a-z0-9/")
  s == s.reverse
end