Example of reversing a linked list in ASP .NET MVC.

HomeController.cs

using System.Diagnostics;
using Microsoft.AspNetCore.Mvc;
using ReverseLinkedListApp.Models;

namespace ReverseLinkedListApp.Controllers;

public class HomeController : Controller
{
    private readonly ILogger<HomeController> _logger;

    public HomeController(ILogger<HomeController> logger)
    {
        _logger = logger;
    }

    [HttpGet]
    public IActionResult Index()
    {
        return View();
    }

    [HttpPost]
    public IActionResult Index(NumbersModel model)
    {
        if (model.Numbers != null)
        {
            var numbers = model.Numbers.Split(",");
            try
            {
                var intNumbers = Array.ConvertAll(numbers, int.Parse);

                //Array.Reverse(intNumbers);

                intNumbers = ReverseNumbers(intNumbers).ToArray();

                var data = new { numbers = intNumbers };
                return Json(data);
            }
            catch
            {
                return BadRequest(new { message = "Error: input must be a comma-separated list of integers." });
            }
        }
        else
        {
            return BadRequest(new { message = "Error: input must be a comma-separated list of integers." });
        }
    }

    public IActionResult Privacy()
    {
        return View();
    }

    [ResponseCache(Duration = 0, Location = ResponseCacheLocation.None, NoStore = true)]
    public IActionResult Error()
    {
        return View(new ErrorViewModel { RequestId = Activity.Current?.Id ?? HttpContext.TraceIdentifier });
    }

    private static IEnumerable<int> ReverseNumbers(int[] numbers)
    {
        Node<int> head = new(numbers.First());
        Node<int> previous = head;

        for (int i=1; i<numbers.Length; i++)
        {
            int number = numbers[i];

            Node<int> node = new(number);
            previous.Next = node;
            previous = node;
        }

        return head.Reverse().ToList();
    }
}

Index.cshtml

@model NumbersModel

@{
    ViewData["Title"] = "Home Page";
}

<div class="text-center">
    <h1 class="display-4">Reverse a Linked List</h1>

    <h3 class="mt-5">Enter Comma-Separated Numbers</h1>
    @using (Html.BeginForm("Index", "Home", FormMethod.Post))
    {
        <div class="mb-3">
            @Html.LabelFor(model => model.Numbers)
            @Html.TextBoxFor(model => model.Numbers, new { @required = "required" })
        </div>
        <button type="submit" class="btn btn-primary">Submit</button>
    }

    <hr>

    <div class="collapse-icon" data-bs-toggle="collapse" data-bs-target="#output-container" title="Toggle output.">
        <i class="bi bi-chevron-down"></i>
    </div>
    <div id="output-container" class="collapse show">
        <div id="output"></div>
    </div>
    <div id="error"></div>
</div>

Node.cs

using System.Collections.Generic;

public class Node<T>
{
    public T? Value { get; set; }
    public Node<T>? Next { get; set; }

    public Node()
    {
    }

    public Node(T value, Node<T>? next = null)
    {
        Value = value;
        Next = next;
    }

    public IEnumerable<T> ToList()
    {
        IList<T> result = new List<T>();

        Node<T>? current = this;
        while (current != null)
        {
            if (current.Value != null)
            {
                result.Add(current.Value);
            }

            current = current.Next;
        }

        return result;
    }

    public Node<T> Reverse()
    {
        Node<T> head = this;
        Node<T>? previous = null;
        Node<T>? current = head;

        while (current != null)
        {
            Node<T>? temp = current.Next;
            current.Next = previous;

            previous = current;
            current = temp;
        }

        return previous != null ? previous : this;
    }
}

NumbersModel.cs

using System.ComponentModel.DataAnnotations;

public class NumbersModel
{
    [Display(Name = "Numbers")]
    [Required]
    public string? Numbers { get; set; }
}

site.css

html {
  font-size: 14px;
}

@media (min-width: 768px) {
  html {
    font-size: 16px;
  }
}

html {
  position: relative;
  min-height: 100%;
}

body {
  margin-bottom: 60px;
}

#error {
  color: darkred;
}

.collapse-icon {
  cursor: pointer;
}

#output {
  background-color: #f8f9fa;
  border: 1px solid #dee2e6;
  border-radius: 0.25rem;
  padding: 1rem;
  min-height: 60px;
}

site.js

$(document).ready(function() {
    $('form').on('submit', function(e) {
        e.preventDefault();

        $('#output').text('');
        $('#error').text('');

        $.ajax({
            url: '/Home/Index',
            type: 'POST',
            data: $(this).serialize(),
            success: function(data) {
                // Get the output div and the toggle icon
                const outputDiv = document.getElementById("output-container");
                $('#output').text(data.numbers);

                // Check if the output div is not currently displayed
                if (outputDiv.style.display === "none" || !outputDiv.classList.contains('show')) {
                    // If it's not displayed, programmatically click the toggle icon.
                    const toggleIcon = document.querySelector(".collapse-icon");
                    toggleIcon.click();
                }
            },
            error: function(data) {
                $('#error').text(data.responseJSON.message);
            }
        });
    });

    $('[data-bs-toggle="collapse"]').click(function() {
        $(this).find("i").toggleClass("bi-chevron-down bi-chevron-right");
    });
});