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#9. Valid PalindromeEasyTwo Pointers

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.

Examples
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 * 10^5
  • s consists only of printable ASCII characters.
Company Frequency
Yandex19Amazon11BCG11CleverTap11Google8Bloomberg7Oracle6Meta5
Prerequisites
Target: O(N) time • O(1) spaceTwo Pointer Convergence
Socratic AI Tutor
Gemini 3.8 Flash
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