#159EasyStrings & Two Pointers· Converging Pointers

Clean Palindrome Check

A name-badge printer wants to flag "mirror" phrases that read the same forwards and backwards, so the badge can get a special frame. Spaces, punctuation and capitalisation must not matter: `"A man, a plan, a canal: Panama"` counts as a mirror phrase. Given a string `s`, ignore every character that is not a letter or a digit and treat uppercase and lowercase letters as equal. Return `true` if what remains is a palindrome, otherwise `false`. A string with no letters or digits at all is considered a palindrome.

Input format

`s`: a string of printable ASCII characters (it contains no double quote and no backslash).

Output format

`true` if the cleaned string reads the same in both directions, otherwise `false`.

Examples

Input: s = "A man, a plan, a canal: Panama"

Output: true

Dropping spaces and punctuation and lowercasing gives "amanaplanacanalpanama", which is a palindrome.

Input: s = "race a car"

Output: false

The cleaned text "raceacar" reads "racaecar" backwards, so it is not a palindrome.

Input: s = " .,"

Output: true

Nothing remains after cleaning, and an empty string counts as a palindrome.

Constraints

0 <= s.length <= 2 * 10^5
s contains printable ASCII characters only; it contains no double quote and no backslash.

Study first

Arrays & Contiguous Memory

#two-pointers
#strings
#palindrome