MaxMin.cs

using System.CodeDom.Compiler;
using System.Collections.Generic;
using System.Collections;
using System.ComponentModel;
using System.Diagnostics.CodeAnalysis;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Runtime.Serialization;
using System.Text.RegularExpressions;
using System.Text;
using System;

class Result
{
    public static int maxMin(int k, List<int> arr) {
        arr.Sort();
        
        var bestUnfairness = int.MaxValue;
        for (var i = 0; i < arr.Count - k + 1; i++) {
            var unfairness = arr[i + k - 1] - arr[i];
            
            if (unfairness < bestUnfairness) bestUnfairness = unfairness;
        }
        
        return bestUnfairness;
    }
}

class Solution
{
    public static void Main(string[] args)
    {
        TextWriter textWriter = new StreamWriter(@System.Environment.GetEnvironmentVariable("OUTPUT_PATH"), true);

        int n = Convert.ToInt32(Console.ReadLine().Trim());

        int k = Convert.ToInt32(Console.ReadLine().Trim());

        List<int> arr = new List<int>();

        for (int i = 0; i < n; i++)
        {
            int arrItem = Convert.ToInt32(Console.ReadLine().Trim());
            arr.Add(arrItem);
        }

        int result = Result.maxMin(k, arr);

        textWriter.WriteLine(result);

        textWriter.Flush();
        textWriter.Close();
    }
}