package main

import (
	"fmt"
	"strings"
)

func isPalindromeOld(s string) bool {
	lower := strings.ToLower(s)
	arr := make([]byte, 0)
	for i := 0; i < len(lower); i++ {
		if (lower[i] >= 'a' && lower[i] <= 'z') || (lower[i] >= '0' && lower[i] <= '9') {
			arr = append(arr, lower[i])
		}
	}
	for i, j := 0, len(arr)-1; i < j; i, j = i+1, j-1 {
		if arr[i] != arr[j] {
			return false
		}
	}
	return true
}

func isAlphanum(c byte) bool {
	lower := c >= 'a' && c <= 'z'
	upper := c >= 'A' && c <= 'Z'
	numeric := c >= '0' && c <= '9'
	return lower || upper || numeric
}

func isEqual(a, b byte) bool {
	if a >= 'a' && a <= 'z' {
		a = a - 'a' + 'A'
	}
	if b >= 'a' && b <= 'z' {
		b = b - 'a' + 'A'
	}
	return a == b
}

func isPalindrome(s string) bool {
	if len(s) == 0 || len(s) == 1 {
		return true
	}
	for beg, end := 0, len(s)-1; beg < end; {
		if !isAlphanum(s[beg]) {
			beg++
			continue
		}
		if !isAlphanum(s[end]) {
			end--
			continue
		}
		if isEqual(s[beg], s[end]) {
			beg++
			end--
		} else {
			return false
		}
	}
	return true
}

func main() {
	fmt.Println(isPalindrome(""))
	fmt.Println(isPalindrome("How are!! ! rawoh~"))
	fmt.Println(isPalindrome("0P"))
}