Valid PalindromeEasy

Valid Palindrome

Easy 9.1k47% acceptance

Two PointersString

Given a string s, return true if it reads the same forwards and backwards once you consider only alphanumeric characters and ignore letter case; otherwise return false.

All non-alphanumeric characters (spaces, punctuation, symbols) are skipped. An empty string — or a string with no alphanumeric characters — counts as a palindrome.

Example 1

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

Output: true

Stripping non-alphanumerics and lowercasing gives "amanaplanacanalpanama", which is a palindrome.

Example 2

Input: s = "race a car"

Output: false

"raceacar" is not a palindrome.

Example 3

Input: s = " "

Output: true

After removing the space there are no characters left, which counts as a palindrome.

Constraints

1 ≤ s.length ≤ 2·10⁵
`s` consists of printable ASCII characters.

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Case 1

"A man, a plan, a canal: Panama"

expected: true

Case 2

"race a car"

expected: false

Case 3

" "

expected: true

Case 4

""

expected: true

Case 5

"0P"

expected: false

Case 6

"ab_a"

expected: true

Case 7

"Was it a car or a cat I saw?"

expected: true