Queue.cs

using System;
using System.Collections.Generic;

namespace Code.QueueDS;

/// <summary>
/// Implement Queue data structure with List.
/// Alternatively, Queue can also be implemented with LinkedList.
/// C# provide Queue<T> class out of the box with performance optimisation.
/// C# Queue is performant because it is implemented using circular array with Head and Tail pointers.
/// and the ability to resize the array when it is full.
/// </summary>
public class Queue<T>
{
    private List<T> items;

    /// <summary>
    /// Constructor to initialize the queue.
    /// </summary>
    /// <param name="data"></param> 
    public Queue()
    {
        items = [];
    }

    /// <summary>
    /// Add an item to the queue.
    /// </summary>
    /// <param name="data"></param>
    public void Enqueue(T data)
    {
        items.Add(data);
    }

    /// <summary>
    /// Remove an item from the queue.
    /// </summary>
    /// <returns></returns>
    /// <exception cref="InvalidOperationException"></exception>
    public T Dequeue()
    {
        if(items.Count == 0)
        {
            throw new InvalidOperationException("Queue is empty");
        }
        T data = items[0];
        items.RemoveAt(0);
        return data;
    }

    /// <summary>
    /// Get the first item from the queue without removing it.
    /// </summary>
    /// <returns></returns>
    /// <exception cref="InvalidOperationException"></exception>
    public T Peek()
    {
        if(items.Count == 0)
        {
            throw new InvalidOperationException("Queue is empty");
        }
        return items[0];
    }

    public int Count => items.Count;
    public bool IsEmpty => items.Count == 0;
    public List<T> Items => items;
}