using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace First_week
{
    public class StringUtils
    {
        public static bool IsPalindrome(string s)
        {
            if (string.IsNullOrEmpty(s))
                return false;

            string cleaned = new string(s.Where(c => char.IsLetterOrDigit(c)).ToArray()).ToLower();
            string reversed = new string(cleaned.Reverse().ToArray());

            return cleaned == reversed;
        }

        public static string ReverseWords(string sentence)
        {
            if (string.IsNullOrEmpty(sentence))
                return sentence;

            var words = sentence.Split(' ');
            var reversedWords = words.Select(word => new string(word.Reverse().ToArray()));

            return string.Join(" ", reversedWords);
        }

        public static string RemovePunctuation(string s)
        {
            if (string.IsNullOrEmpty(s))
                return s;

            return new string(s.Where(c => !char.IsPunctuation(c)).ToArray());
        }

        public static bool IsAlphaNumeric(string s)
        {
            if (string.IsNullOrEmpty(s))
                return false;

            return s.All(char.IsLetterOrDigit);
        }
    }
}