DSA18.py

# Question --->

# 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.

# Answer ---->

class Solution(object):
    def isPalindrome(self, s):
        left, right = 0, 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

# Result --->

# Your input:
# "A man, a plan, a canal: Panama"

# Output:
# true

# Expected:
# true