Udemy: Master Coding Interview - Stacks + Queues - #114

using System;

public class Node {
    public Node next;
    public string value;
    public Node(string value) {
        this.value = value;
    }
}

class Stack {
    Node top;
    Node bottom;
    int length = 0;
    
    static void Main() {
        Console.WriteLine("Hello World!");
        
        Stack myStack = new Stack();
        Console.WriteLine("myStack: " + myStack.ToString());
        myStack.Push("Discord");
        Console.WriteLine("myStack: " + myStack.ToString());
        myStack.Push("Udemy");
        Console.WriteLine("myStack: " + myStack.ToString());
        myStack.Push("Google");
        Console.WriteLine("myStack: " + myStack.ToString());
        Console.WriteLine("myStack.Peek(): " + myStack.Peek());
        Console.WriteLine("myStack: " + myStack.ToString());
        myStack.Pop();
        Console.WriteLine("myStack: " + myStack.ToString());
        myStack.Pop();
        Console.WriteLine("myStack: " + myStack.ToString());
        myStack.Pop();
        Console.WriteLine("myStack: " + myStack.ToString());
    }
    
    public void Push(string value) {
        Node item = new Node(value);
        if (this.length == 0) {
            this.bottom = item;
        }
        if (this.top != null) {
            item.next = this.top;
        }
        this.length++;
        this.top = item;
    }
    
    public string Pop() {
        if (this.top != null) {
            string value = this.top.value;
            this.top = this.top.next;
            this.length--;
            return value;
        }
        return null;
    }
    
    public string Peek() {
        if (this.top != null) {
            return this.top.value;
        }
        return null;
    }
    
    public string ToString() {
        string s = "{";
        Node current = this.top;
        int count = 0;
        while (current != null) {
            if (count > 0) {
                s += ", ";
            }
            count++;
            s += "" + current.value;
            current = current.next;
        }
        s += "}";
        return s;
    }
}