[PYTHON] LeetCode Solved: Valid Palindrome

Palindrome is a palindrome https://leetcode.com/problems/valid-palindrome/

Problem statement:

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.

Find out if the given sentence is a palindrome. However, ignore everything except alphanumeric characters (spaces, periods, symbols, etc.). Suppose an empty string is a palindrome. . . . . . .

This time we have to extract only alphanumeric characters. I thought it was okay because I couldn't use the regular expression library, but there is a method called isalnum. I did not know.... Answer 1: Try turning it obediently with a for sentence.


class Solution:
    def isPalindrome(self, s: str) -> bool:
        alphanumeric_filter = filter(str.isalnum, s)
        alphanumeric_string = "".join(alphanumeric_filter).lower()
        reverse_text = ""
        for i in range(1,len(alphanumeric_string)+1):
             reverse_text += alphanumeric_string[len(alphanumeric_string)-i]
        return alphanumeric_string == reverse_text:

Answer 2: Lambda style is neat. Reverse is also treated as a list and processed in one line for a clean look.


class Solution:
    def isPalindrome(self, s: str) -> bool:

        filtered = filter(lambda ch: ch.isalnum(), s)
        lowercase = map(lambda ch: ch.lower(), filtered)

        processed_list = list(lowercase)
        reversed_list = processed_list[::-1]

        return processed_list == reversed_list

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