[Swift] Valid Palindrome

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.

풀러가기

문제 이해

코드

func isPalindrome(_ s: String) -> Bool {
  var arr = Array(s)
  var left = 0
  var right = s.count - 1
  
  while left < right {
    var first = arr[left]
    var last = arr[right]
    
    if !first.isLetter && !first.isNumber {
      left += 1
    } else if !last.isLetter && !last.isNumber {
      right -= 1
    } else if first.lowercased() == last.lowercased() {
      left += 1
      right -= 1
    } else {
      return false
    }
  }
  
  return true
}

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