using System;

using System.Collections.Generic;

​

            // You are given an array of n integers and a number 'target'. 

            // Write a function that determins whether there is a pair of elements in the array that sums to exactly target. 

            // For example, given the array [1, 3, 7] and k = 8, the answer is “yes,” but given k = 6 the answer is “no.”

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine(IsSumOfTwo(new List<int> { 1, 3, 7 }, 7));

        Console.WriteLine(IsSumOfTwo(new List<int> { 1, 3, 7 }, 8));

        Console.WriteLine(IsSumOfTwo(null, 7));

        Console.WriteLine(IsSumOfTwo(new List<int> { 3, 5, 2, -4, 8, 11 }, 19));

        Console.WriteLine(IsSumOfTwo(new List<int>(), 7));

        Console.WriteLine(IsSumOfTwo(new List<int> { 3, 5, 2, -4, 8, 8, 11 }, 19));

        Console.WriteLine(IsSumOfTwo(new List<int> { 3, 5, 2, -4, 8, 8, 11 }, 20));

    }

​

    static bool IsSumOfTwo(List<int> arr, int target)

    {

        // fill me in

​

​

        return false;

    }

}