Convert Number and Array pair sum to given

gistfile1.txt

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

namespace ConsoleApp1
{
    //https://codeworldtechnology.wordpress.com/2017/01/07/find-all-pair-of-array-of-integers-whose-sum-is-equal-to-a-given-number-in-c/
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(GetString(0));
            Console.WriteLine(GetString(5));
            Console.WriteLine(GetString(10));
            var data = 123456789;
            var data1 = data.ToString();
            Console.WriteLine(GetString(123456789));
            // var result1 = canSum(new[] { 7, 8, 1, 4, 6 }, 15);
            var result = canSum(new[] { 1, 4, 6, 7, 8 }, 15);    
            var result1 = Find(new[] { 1, 4, 6, 7, 8 }, 15);
            Console.WriteLine(result == true);

            int[] arr = { 2, 4, 3, 5, 6, -2, 4, 7, 8, 9 };
            int n = 7;
            PrintPairs(arr, n);

            Console.ReadKey();
        }

        static string[] words = "Zero,One,Two,Three,Four,Five,Six,Seven,Eight,Nine,Ten".Split(',');

        public static string GetString(int value)
        {
            // See if the number can easily be represented by an English word.
            // ... Otherwise, return the ToString result.
            if (value >= 0 && value <= 10)
            {
                return words[value];
            }
            return value.ToString();
        }
   
    static bool canSum(int[] nums, int target)
        {
            var set = new HashSet<int>(nums);
            //var pair = nums.Where(n => set.Contains(target - n)));

            return nums.Any(n => set.Contains(target - n));

            //for (int i = 0; i < nums.Length; i++)
            //{
            //    for (int j = i + 1; j < nums.Length; j++)
            //    {
            //        if ((nums[i] + nums[j]) == target) return true;
            //    }
            //}
            //return false;
        }

        private static void PrintPairs(int[] arr, int n)
        {
            List<int> arrayItemList = new List<int>();
            foreach (var item in arr)
            {
                int remainingvalue = n - item;
                if (arrayItemList.Contains(remainingvalue))
                {
                    Console.WriteLine($"({ item},{remainingvalue})");
                }
                else
                {
                    arrayItemList.Add(item);
                }
            }
        }
        
        public class MatchingPairs
        {
            public int lower;
            public int upper;
        }

        static List<MatchingPairs> Find(int[] array, int sumToFind)
        {
            var query = from f in array
                        from g in array
                        where (f < g) && (f + g == sumToFind)
                        select new MatchingPairs { lower = f, upper = g };

            return query.ToList();
        }
    }
}