Algorithms - 1. Merge Sort

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

namespace Algorithms
{
    class Program
    {
        static void Sort(int[] arr, int startIndex, int endIndex)
        {
            if (startIndex >= endIndex)
            {
                return;
            }

            int midIndex = (startIndex + endIndex) / 2;

            Sort(arr, startIndex, midIndex);
            Sort(arr, midIndex + 1, endIndex);

            Merge(arr, startIndex, midIndex, endIndex);
        }

        private static void Merge(int[] arr, int startIndex, int midIndex, int endIndex)
        {
            if (midIndex < 0 || midIndex + 1 >= arr.Length
                || arr[midIndex] <= arr[midIndex + 1])
            {
                return;
            }

            int[] tempArr = new int[arr.Length];

            for (int i = startIndex; i <= endIndex; i++)
            {
                tempArr[i] = arr[i];
            }

            int leftIndex = startIndex;
            int rightIndex = midIndex + 1;

            for (int i = startIndex; i <= endIndex; i++)
            {
                if (leftIndex > midIndex)
                {
                    arr[i] = tempArr[rightIndex];
                    rightIndex++;

                    // arr[i] = tempArr[rightIndex++]; - кратък запис на горните 2
                }

                else if (rightIndex > endIndex)
                {
                    arr[i] = tempArr[leftIndex++];
                }

                else if (tempArr[leftIndex] <= tempArr[rightIndex])
                {
                    arr[i] = tempArr[leftIndex++];
                }

                else
                {
                    arr[i] = tempArr[rightIndex++];
                }
            }
        }

        static void Main(string[] args)
        {

            var numbers = Console.ReadLine().Split().Select(int.Parse).ToArray();

            Sort (numbers, 0, numbers.Length - 1);

            Console.WriteLine(string.Join(" ", numbers));
        }

    }
}