20 -- validate palindrome string

1. subject

Given a string , Verify that it is a palindrome string , Consider only alphabetic and numeric characters , The case of letters can be ignored .
explain ： In this question , We define an empty string as a valid palindrome string .
Example 1:
Input : “A man, a plan, a canal: Panama”
Output : true
explain ：“amanaplanacanalpanama” It's a palindrome string
Example 2:
Input : “race a car”
Output : false
explain ：“raceacar” It's not a palindrome string

• Pay attention to the examination — Alphanumeric characters

2. Ideas

Double pointer

    func isPalindrome(_ s: String) -> Bool {
        let nums: [String.Element] = ["0","1","2","3","4","5","6","7","8","9"]

	//  Here is higher-order grammar 
        let tempArr: [String.Element] = Array(s.lowercased()).reduce(into: []) { partialResult, char in
            if char >= "a" && char <= "z" || nums.contains(char) {
                partialResult.append(char)
            }
        }
//        print(tempArr)
        
        var left = 0, right = tempArr.count - 1
        
        while left <= right {
            if tempArr[left] == tempArr[right] {
                left += 1
                right -= 1
            } else {
                return false
            }
        }
        
        return true
    }