Quick Sort in C#

Quick Sort

in C#

Welcome to the Quick 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);
QuickSort(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;
}

static void QuickSort(Span<int> span)
{
    if (span.Length <= 1)
        return;

    int lo = 0;
    int hi = span.Length - 1;

    Sort(span, lo, hi);

    static void Sort(Span<int> s, int lo, int hi)
    {
        while (lo < hi)
        {
            int p = Partition(s, lo, hi);

            // Tail recursion elimination: sort smaller side first
            if (p - lo < hi - p)
            {
                Sort(s, lo, p - 1);
                lo = p + 1;
            }
            else
            {
                Sort(s, p + 1, hi);
                hi = p - 1;
            }
        }
    }

    static int Partition(Span<int> s, int lo, int hi)
    {
        int pivot = s[hi];
        int i = lo;

        for (int j = lo; j < hi; j++)
        {
            if (s[j] <= pivot)
            {
                (s[i], s[j]) = (s[j], s[i]);
                i++;
            }
        }

        (s[i], s[hi]) = (s[hi], s[i]);
        return i;
    }
}

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;
}

Quick 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.