ValidPalindrome

Problem

https://leetcode.com/problems/valid-palindrome/

Solution

First, we convert s to all lowercase. Rather than remove all non-alphanumeric characters, we can ignore them when checking if s is a palindrome. We do this by using two pointers i and j at the beginning of s and at the end of s. When both pointers are on non-alphanumeric characters, move them inwards.

Code

https://github.com/GeorgeRPu/tech-interview-prep/blob/main/solutions/ValidPalindrome.py

def isPalindrome(s: str) -> bool:
    """Check if ``s`` is a palindrome, ignoring non-alphanumeric characters.
    """
    s = s.lower()

    i = 0
    j = len(s) - 1
    while i < j:
        if not s[i].isalnum():
            i += 1
        elif not s[j].isalnum():
            j -= 1
        elif s[i] != s[j]:
            return False
        else:
            i += 1
            j -= 1
    return True

Test

>>> from ValidPalindrome import isPalindrome
>>> isPalindrome('A man, a plan, a canal: Panama')
True
>>> isPalindrome('race a car')
False
>>> isPalindrome(' ')
True
>>> isPalindrome('0P')
False

Functions

isPalindrome(s)

Check if s is a palindrome, ignoring non-alphanumeric characters.