Solutions

# Check if the reversed string is equal to the original string. Or use two pointers to compare characters.
# two-pointers

# O(n) time, O(n) space

# Reverse string
def is_palindrome(s: str) -> bool:
    newstr = ''
    for c in s:
        if str.isalnum(c):
            newstr += c.lower()
    return newstr == newstr[::-1]

# Two pointers
def is_palindrome(s: str) -> bool:
    left = 0
    right = len(s) - 1
    while left < right:
        while left < right and not s[left].isalnum():
            left += 1
        while left < right and not s[right].isalnum():
            right -= 1
        if s[left].lower() != s[right].lower():
            return False
        left += 1
        right -= 1
    return True