Checks if a given array contains the specified item using divide & conquer

program.cs

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

namespace ConsoleApp1
{
    class Program
    {
        private static ContainsCheckerDnQ<int> containsChecker = new ContainsCheckerDnQ<int>();
        private static SortedContainsCheckerDnQ<int> sortedContainsChecker = new SortedContainsCheckerDnQ<int>();

        static void Main(string[] args)
        {
            int[] items = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
            PrintContains(7, items, containsChecker);
            PrintContains(5, items, containsChecker);
            PrintContains(3, items, containsChecker);
            PrintContains(-1, items, containsChecker);
            PrintContains(0, items, containsChecker);
            PrintContains(10, items, containsChecker);
            PrintContains(11, items, containsChecker);

            PrintContains(7, items, sortedContainsChecker);
            PrintContains(5, items, sortedContainsChecker);
            PrintContains(3, items, sortedContainsChecker);
            PrintContains(-1, items, sortedContainsChecker);
            PrintContains(0, items, sortedContainsChecker);
            PrintContains(1, items, sortedContainsChecker);
            PrintContains(10, items, sortedContainsChecker);
            PrintContains(11, items, sortedContainsChecker);
        }

        private static void PrintContains(int item, int[] items, IContainsChecker<int> checker)
        {
            Console.WriteLine("Checking " + item);
            var exists = checker.Contains(item, items);
            Console.WriteLine(exists ?
                "It's there!" : 
                "It isn't there!");
            Console.WriteLine("\n\n");
        }
    }

    interface IContainsChecker<T> where T : IComparable
    {
        bool Contains(T item, T[] items);
    }

    class ContainsCheckerDnQ<T> : IContainsChecker<T> where T : IComparable
    {
        public bool Contains(T item, T[] items)
        {
            Console.WriteLine($"Checking if {item} exists in {string.Join(",", items)}");
            if (items.Length == 0) return false;
            if (items.Length == 1) return items[0].CompareTo(item) == 0;

            var left = new T[items.Length / 2];
            var right = new T[items.Length - left.Length];
            for (int i = 0; i < left.Length; i++)
            {
                left[i] = items[i];
            }
            for (int i = 0; i < right.Length; i++)
            {
                right[i] = items[left.Length + i];
            }
            return Contains(item, left) || Contains(item, right);
        }
    }

    class SortedContainsCheckerDnQ<T> : IContainsChecker<T> where T : IComparable
    {
        public bool Contains(T item, T[] items)
        {
            return ContainsHelper(item, items, 0, items.Length);
        }

        private bool ContainsHelper(T item, T[] items, int min, int max)
        {
            if (min > max) return false;
            if (min == max && min == items.Length) return items[min - 1].CompareTo(item) == 0;

            var mid = (max + min) / 2;
            var comparingElement = items[mid];
            var comp = item.CompareTo(comparingElement);
            if (comp == -1)
            {
                return ContainsHelper(item, items, min, mid - 1);
            }
            else if (comp == 1)
            {
                return ContainsHelper(item, items, mid + 1, max);
            }
            return true;
        }
    }
}