0125-valid-palindrome

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Description

A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forward and backward. Alphanumeric characters include letters and numbers.

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

 

Example 1:

Input: s = "A man, a plan, a canal: Panama"
Output: true
Explanation: "amanaplanacanalpanama" is a palindrome.

Example 2:

Input: s = "race a car"
Output: false
Explanation: "raceacar" is not a palindrome.

Example 3:

Input: s = " "
Output: true
Explanation: s is an empty string "" after removing non-alphanumeric characters.
Since an empty string reads the same forward and backward, it is a palindrome.

 

Constraints:

• 1 <= s.length <= 2 * 105
• s consists only of printable ASCII characters.

Solution(Python)

class Solution:
    def isPalindrome(self, s: str) -> bool:
        return self.two_pointers(s)
    # Time Complexity: O(n)
    # Space complexity: O(n)
    def simulation(self, s):
        filtyered_char = filter(lambda ch:ch.isalnum(), s)
        lowercase_chars = map(lambda ch: ch.lower(),s )

        return lowercase_chars == lowercase_chars[::-1]

    # Time Complexity: O(n)
    # Space complexity: O(1)
    def two_pointers(self, s):
        i,j = 0, len(s) - 1
        while i<j:
            while i<j and not s[i].isalnum():
                i+=1

            while j>i and not s[j].isalnum():
                j-=1
            if s[i].lower() != s[j].lower():
                return False
            i+=1
            j-=1
        return True