Добавьте файлы проекта.

StringUtils.cs

@@ -0,0 +1,43 @@
+namespace First_week
+{
+    internal 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);
+        }
+    }
+}