[NeetCode 150] Is Palindrome

Is Palindrome

Given a string s, return true if it is a palindrome, otherwise return false.

A palindrome is a string that reads the same forward and backward. It is also case-insensitive and ignores all non-alphanumeric characters.

Example 1:

Input: s = "Was it a car or a cat I saw?"

Output: true

Explanation: After considering only alphanumerical characters we have “wasitacaroracatisaw”, which is a palindrome.

Example 2:

Input: s = "tab a cat"

Output: false

Explanation: “tabacat” is not a palindrome.

Constraints:

1 <= s.length <= 1000

s is made up of only printable ASCII characters.

Solution

Easy problem! First, we need to filter all non-alphanumeric characters out. Then just check if this string is a palindrome one character by one character.

Oh, because palindrome is case-insensitive, we can convert the string into lower case at very first.

Code

To appear like an expert, we can use regular expression to find all alpha and numeric characters.

class Solution:
    def isPalindrome(self, s: str) -> bool:
        s = s.lower()
        alphanumeric_string = ''.join(re.findall(r'[a-z0-9]+', s))
        for i in range(len(alphanumeric_string)//2):
            if alphanumeric_string[i] != alphanumeric_string[-1-i]:
                return False
        return True