using System;

using System.Linq;

​

namespace ConsoleApplication1

{

    public class Program

    {

        public static void Main(string[] args)

        {

            CheckHi("The child wanted to play in the mud");

            CheckHi("Hi there");

            CheckHi("Hector had a hip problem");      

            CheckHi("He said, 'Hi, how are you?'");

        }

        private static void CheckHi(string sentence)

        {

            var punctuation = sentence.Where(Char.IsPunctuation).Distinct().ToArray();

            var words = sentence.Split().Select(x => x.Trim(punctuation));

            var containsHi = words.Contains("hi", StringComparer.OrdinalIgnoreCase);

            Console.WriteLine("{0}: {1}", containsHi, sentence);

        }

    }

}

​

​