125. Valid Palindrome

Easy
Two Pointers String

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 * 10^5
  • s consists only of printable ASCII characters.
func isPalindrome(s string) bool {
	s = strings.ToLower(s)
	ss := ""
	for _, c := range s {
		if (c >= 'a' && c <= 'z') || (c >= '0' && c <= '9') {
			ss += string(c)
		}
	}
	for i := 0; i < len(ss)/2; i++ {
		if ss[i] != ss[len(ss)-i-1] {
			return false
		}
	}
	return true
}