#nullable enable

​

using System;

using System.Collections.Generic;

using System.Linq;

using System.IO;

using System.Threading.Tasks;

using System.Net.Http;

using System.Text;

​

RecursiveStructure data = new() // 0

{

    Inner = new() // 1

    {

        Inner = new() // 2

        {

            Inner =  null // 3 -- ignored

        }

    }

};

​

NormalRecursion(data);

Console.WriteLine();

QueueRecursion(data);

Console.WriteLine();

StackRecursion(data);

​

void NormalRecursion(RecursiveStructure data, int depth = 0)

{

    // actual recursive logic below

    Console.WriteLine($"NR depth {depth}");

    if (data.Inner is RecursiveStructure inner)

        NormalRecursion(inner, ++depth);

}

​

void QueueRecursion(RecursiveStructure data, int depth = 0)

{

    var queue = new Queue<(RecursiveStructure, int)>();

    queue.Enqueue((data, depth));

    while (queue.Any())

    {

        var (currentData, currentDepth) = queue.Dequeue();

        // actual recursive logic below

        Console.WriteLine($"QR depth {currentDepth}");

        if (currentData.Inner is RecursiveStructure inner)

            queue.Enqueue((inner, ++currentDepth));

    }

}

​

void StackRecursion(RecursiveStructure data, int depth = 0)

{

    var stack = new Stack<(RecursiveStructure, int)>();

    stack.Push((data, depth));

    while (stack.Any())

    {

        var (currentData, currentDepth) = stack.Pop();

        // actual recursive logic below

        Console.WriteLine($"SR depth {currentDepth}");

        if (currentData.Inner is RecursiveStructure inner)

            stack.Push((inner, ++currentDepth));

    }

}

​

​

class RecursiveStructure

{

    public RecursiveStructure? Inner {get; init;}   

}

​