Find if pair of elements with given sum exists in large integer array

Question

I\'m having a integer array of 10 Million elements, how to write a function in C# which returns True if the array has a pair which sums up to 75.

My code is:

Answer 1

using System;
using System.Diagnostics;
using System.Linq;
using System.Collections.Generic;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            const int max = 10000000;
            const int sum = 75;

            var data = new int[max];

            var rnd = new Random();

            bool found = false; 
            int c = 1;
            Stopwatch sw;

            while (!found)
            {
                sw = Stopwatch.StartNew();
                for (int i = 0; i < max; ++i)
                {
                    data[i] = rnd.Next(0, max*25);
                }
                sw.Stop();
                Console.WriteLine("Took {0}ms to create the array", sw.ElapsedMilliseconds);

                sw = Stopwatch.StartNew();
                var check75 = new HashSet(data.Where(x => x <= 75));
                sw.Stop();
                Console.WriteLine("Took {0}ms to create the hashset", sw.ElapsedMilliseconds);

                sw = Stopwatch.StartNew();
                for (int i = 0; i < max; ++i)
                {
                    if (check75.Contains(sum - data[i]))
                    {
                        Console.WriteLine("{0}, {1} ", i, data[i]);
                        found = true;
                    }
                }
                sw.Stop();
                Console.WriteLine("Took {0}ms to check75", sw.ElapsedMilliseconds);

                Console.WriteLine("Loop #" + c++);
            }
            Console.WriteLine("Finish");
            Console.ReadKey();
        }
    }
}