Valid palindrome

Leetcode 125 problem.

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.

Go

Time complexity: $O(n)$ - n is a length of a string
Auxiliary space: $O(n)$ - n is a length of a string

import "strings"

func extractAlphaNumChars(s string) string {
    var result strings.Builder

    for i := 0; i < len(s); i++ {
        char := s[i]
        if ('a' <= char && char <= 'z') ||
            ('A' <= char && char <= 'Z') ||
            ('0' <= char && char <= '9') {
            result.WriteByte(char)
        }
    }
    return result.String()
}

func reverseString(s string) string {
    chars := []rune(s)
    for i, j := 0, len(chars)-1; i < j; i, j = i+1, j-1 {
        chars[i], chars[j] = chars[j], chars[i]
    }
    return string(chars)
}

func isPalindrome(s string) bool {
    text := extractAlphaNumChars(s)
    text = strings.ToLower(text)

    return text == reverseString(text)
}

thoughtbook

Valid palindrome

Go