using System;

using System.Collections.Generic;

public class Program

{

    class Node {

        public string Label { get; }

        public Node[] Children { get; }

        public Node(string label, Node child) 

        {

            Label = label;

            Children = new [] { child };

        }

        public Node(string label, Node[] children = null) 

        {

            Label = label;

            Children = children ?? new Node[0];

        }

    }

    public static void Main()

    {

        var graphRoot = new Node("A", new [] {

                            new Node("B", 

                                new Node("C")),

                            new Node("D")});

        BreadthFirstSearch(graphRoot);

        DepthFirstSearch(graphRoot);

    }

    static void BreadthFirstSearch(Node root) 

    {

        Console.Write("BFS: ");

        var queue = new Queue<Node>();

        queue.Enqueue(root);

        while (queue.Count != 0) {

            var current = queue.Dequeue();

            Console.Write(current.Label + " ");

            foreach (var child in current.Children) {

                queue.Enqueue(child);

            }

        }

        Console.WriteLine();

    }

    static void DepthFirstSearch(Node root) 

    {

        Console.Write("DFS: ");

        var stack = new Stack<Node>();

        stack.Push(root);

        while (stack.Count != 0) {

            var current = stack.Pop();

            Console.Write(current.Label + " ");

            foreach (var child in current.Children) {

                stack.Push(child);

            }

        }

        Console.WriteLine();

    }

}