02_ValidPalindrome.py

# Question link - https://leetcode.com/problems/valid-palindrome/description/?envType=study-plan-v2&envId=top-interview-150

class Solution:
    def isPalindrome(self, s: str) -> bool:
        # SOl2 - uses pointer appoarch with helper func alphaNum() 
        l , r = 0 , len(s) - 1

        while l < r:
            # check left char is alphnaNum , not then increment l
            while l<r and not self.alphaNum(s[l]):
                l += 1
            # check right char is alphnaNum ,not  then decrement r
            while l<r and not self.alphaNum(s[r]):
                r -= 1

            if s[l].lower() != s[r].lower():
                return False
            l , r = l + 1 , r - 1
        return True 

    def alphaNum(self, c):
        # this function checks for alphanum characters return True
        return (ord('A') <= ord(c) <= ord('Z')
               or ord('a') <= ord(c) <= ord('z')
               or ord('0') <= ord(c) <= ord('9'))
    

        # # Sol 1 
        # newStr = "" #Creating a new string 

        # # Traverse the string and if it is alnum then convert to lowercase 
        # for c in s:
        #     if c.isalnum():
        #         newStr += c.lower()
        # # Return True , if palindrome otherwise false
        # return newStr == newStr[::-1]