programming-examples/c-sharp/Sorting/C# Sharp program to sort a list of elements using Merge sort.cs

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

namespace Merge_sort
{
class Program
{
    static void Main(string[] args)
    {
        List<int> unsorted = new List<int>();
        List<int> sorted;
        Random random = new Random();
        Console.WriteLine("Original array elements:" );
        for(int i = 0; i< 10; i++)
            {
                unsorted.Add(random.Next(0,100));
                Console.Write(unsorted[i]+" ");
            }
        Console.WriteLine();
        sorted = MergeSort(unsorted);
        Console.WriteLine("Sorted array elements: ");
        foreach (int x in sorted)
            {
                Console.Write(x+" ");
            }
        Console.Write("\n");
    }


    private static List<int> MergeSort(List<int> unsorted)
    {
        if (unsorted.Count <= 1)
            return unsorted;
        List<int> left = new List<int>();
        List<int> right = new List<int>();
        int middle = unsorted.Count / 2;
        for (int i = 0; i < middle; i++) //Dividing the unsorted list
            {
                left.Add(unsorted[i]);
            }
        for (int i = middle; i < unsorted.Count; i++)
            {
                right.Add(unsorted[i]);
            }
        left = MergeSort(left);
        right = MergeSort(right);
        return Merge(left, right);
    }

    private static List<int> Merge(List<int> left, List<int> right)
    {
        List<int> result = new List<int>();
        while(left.Count > 0 || right.Count>0)
            {
                if (left.Count > 0 && right.Count > 0)
                    {
                        if (left.First() <= right.First())  //Comparing First two elements to see which is smaller
                            {
                                result.Add(left.First());
                                left.Remove(left.First());      //Rest of the list minus the first element
                            }
                        else
                            {
                                result.Add(right.First());
                                right.Remove(right.First());
                            }
                    }
                else if(left.Count>0)
                    {
                        result.Add(left.First());
                        left.Remove(left.First());
                    }
                else if (right.Count > 0)
                    {
                        result.Add(right.First());
                        right.Remove(right.First());
                    }
            }
        return result;
    }
}
}