Merge Sort in C#

Merge Sort

in C#

Welcome to the Merge Sort in C# page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

using System.Collections.Generic;
using System.Runtime.InteropServices;
using System.Buffers;

if (args is not [var input] || !TryParseList(input.AsSpan(), out var numbers))
    return ExitWithUsage();

Span<int> span = CollectionsMarshal.AsSpan(numbers);
MergeSort(span);

Console.WriteLine(string.Join(", ", numbers));
return 0;

static bool TryParseList(ReadOnlySpan<char> span, out List<int> numbers)
{
    numbers = new(span.Count(',') + 1);

    while (!span.IsEmpty)
    {
        int comma = span.IndexOf(',');
        var token = comma >= 0 ? span[..comma] : span;

        span = comma >= 0 ? span[(comma + 1)..] : [];

        if (!int.TryParse(token, out int n))
            return false;

        numbers.Add(n);
    }

    return numbers.Count > 1;
}

// Bottom-up merge sort
static void MergeSort(Span<int> span)
{
    int n = span.Length;
    if (n <= 1)
        return;

    int[] buffer = new int[n];

    Span<int> src = span;
    Span<int> dst = buffer;

    for (int width = 1; width < n; width *= 2)
    {
        for (int left = 0; left < n; left += width * 2)
        {
            int mid = Math.Min(left + width, n);
            int right = Math.Min(left + width * 2, n);

            Merge(
                src[left..mid],
                src[mid..right],
                dst[left..right]
            );
        }

        Span<int> temp = src;
        src = dst;
        dst = temp;
    }

    // if final data ended up in buffer, copy back
    if (!src.Overlaps(span))
        src.CopyTo(span);
}

static void Merge(
    ReadOnlySpan<int> left,
    ReadOnlySpan<int> right,
    Span<int> target)
{
    int li = 0;
    int ri = 0;
    int ti = 0;

    while (li < left.Length && ri < right.Length)
    {
        target[ti++] = left[li] <= right[ri]
            ? left[li++]
            : right[ri++];
    }

    left[li..].CopyTo(target[ti..]);
    right[ri..].CopyTo(target[ti..]);
}

static int ExitWithUsage()
{
    Console.WriteLine(
        "Usage: please provide a list of at least two integers to sort in the format \"1, 2, 3, 4, 5\""
    );
    return 1;
}

Merge Sort in C# was written by:

• Parker Johansen
• Ștefan-Iulian Alecu

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

No 'How to Implement the Solution' section available. Please consider contributing.

How to Run the Solution

No 'How to Run the Solution' section available. Please consider contributing.