Custom Implementation of Lists

using System; // This is required for the exception.
 
public class CList<T>
{
  // A CList is … a Cell.
  private Cell first;
 
  // By default, a CList contains only an empty cell.
  public CList()
  {
    first = null;
  }
 
  // A Cell is itself two things:
  // - An element of data (of type T),
  // - Another cell, containing the next element of data.
  // We implement this using automatic properties:
  private class Cell
  {
    public T Data { get; set; }
    public Cell Next { get; set; }
 
    public Cell(T dataP, Cell nextP)
    {
      Data = dataP;
      Next = nextP;
    }
  }
 
  // A method to add a cell at the beginning
  // of the CList (to the left).
  // We call it AddF for "Add First".
 
  public void AddF(T dataP)
  {
    first = new Cell(dataP, first);
  }
 
  // A method to add a cell at the end
  // of the CList (to the right).
  // We call it AddL for "Add Last".
 
  public void AddL(T dataP)
  {
    if (first == null)
      AddF(dataP);
    else
    {
      Cell cCell = first;
      while (cCell.Next != null)
      // As long as the cCell Cell has a neighbour…
      {
        cCell = cCell.Next;
        // We move the cCell cell to this neighbour.
      }
      // When we are done, we can insert the cell.
      cCell.Next = new Cell(dataP, null);
    }
  }
 
  // We will actually frequently test if
  // a CList is empty, so we might
  // as well introduce a method for that:
 
  public bool IsEmpty()
  {
    return (first == null);
  }
 
  // Accessor for the size of the CList.
  public int Size
  {
    get
    {
      int size;
      if (IsEmpty())
      {
        size = 0;
      }
      else
      {
        size = 1;
        Cell cCell = first;
        while (cCell.Next != null)
        // As long as the cCell Cell has a neighbour…
        {
          cCell = cCell.Next;
          // We move the cCell cell to this neighbour.
          size++;
        }
      }
      return size;
    }
  }
 
  // We can implement a ToString method
  // "the usual way", using a loop
  // similar to the one in AddL:
  // (But we make it very fancy, as
  //  if we were drawing an array).
 
  public override string ToString()
  {
    string returned = "";
    for (int i = 0; i < Size; i++)
    {
      returned += "————";
    }
    returned += "\n| ";
    Cell cCell = first;
    while (cCell != null)
    {
      returned += $"{cCell.Data} | ";
      cCell = cCell.Next;
    }
    returned += "\n";
    for (int i = 0; i < Size; i++)
    {
      returned += "————";
    }
    return returned;
  }
 
  // Method to obtain the nth element if it exists.
  public T Access(int index)
  {
    if (index >= Size)
    {
      throw new IndexOutOfRangeException();
    }
    else // Some IDE will flag this "else" as redundant.
    {
      int counter = 0;
      Cell cCell = first;
      while (counter < index)
      {
        cCell = cCell.Next;
        counter++;
      }
      return cCell.Data;
    }
  }
 
  /*
   * We can write four methods to
   * remove elements from a CList.
   * - One that clears it entirely,
   * - One that removes the first cell,
   * - One that removes the last cell,
   * - One that removes the nth cell, if it exists,
   */
 
  public void Clear()
  {
    first = null;
  }
 
  public void RemoveF()
  {
    if (!IsEmpty())
      first = first.Next;
  }
 
  public void RemoveL()
  {
    if (!IsEmpty())
    {
      if (first.Next == null)
      {
        RemoveF();
      }
      else
      {
        Cell cCell = first;
        while (
          cCell.Next != null && cCell.Next.Next != null
        )
        {
          cCell = cCell.Next;
        }
 
        cCell.Next = null;
      }
    }
  }
 
  // Method to remove the nth element if it exists.
  public void RemoveI(int index)
  {
    if (index > Size)
    {
      throw new IndexOutOfRangeException();
    }
    else // Some IDE will flag this "else" as redundant.
    {
      int counter = 0;
      Cell cCell = first;
      while (counter < index - 1)
      {
        cCell = cCell.Next;
        counter++;
      }
      cCell.Next = cCell.Next.Next;
    }
  }
 
  // Method to obtain the largest
  // number of consecutive values
  // dataP.
 
  public int CountSuccessive(T dataP)
  {
    int cCount = 0;
    int mCount = 0;
    Cell cCell = first;
    while (cCell != null)
    {
      if (cCell.Data.Equals(dataP))
      {
        cCount++;
      }
      else
      {
        if (cCount > mCount)
        {
          mCount = cCount;
        }
        cCount = 0;
      }
      cCell = cCell.Next;
    }
    if (cCount > mCount)
    {
      mCount = cCount;
    }
    return mCount;
  }
 
  // Method to remove at a particular index
  // Very similar to RemoveI, simply
  // implemented with a different philosophy.
  public void RemoveAt(int index)
  {
    if (index >= 0 && index < Size)
    {
      if (index == 0)
        RemoveF();
      else if (index == (Size - 1))
        RemoveL();
      else
      {
        Cell cCell = first;
        for (int i = 0; i < index - 1; i++)
        {
          cCell = cCell.Next;
        }
        cCell.Next = cCell.Next.Next;
      }
    }
    else
      throw new ArgumentOutOfRangeException();
  }
 
  // Method to reverse a list
  public void Reverse()
  {
    Cell cCell = first;
    Cell previous = null;
    Cell next;
    while (cCell != null)
    {
      next = cCell.Next;
      cCell.Next = previous;
      previous = cCell;
      cCell = next;
    }
    first = previous;
  }
 
  // Method to look for a specific value (recursively)
  public bool Find(T dataP)
  {
    return Find(first, dataP);
  }
 
  private bool Find(Cell cCell, T dataP)
  {
    if (cCell == null)
      return false;
    else if (cCell.Data.Equals(dataP))
      return true;
    else
      return Find(cCell.Next, dataP);
  }
 
  // Method to obtain the last index
  // of dataP.
  public int LastIndexOf(T dataP)
  {
    int index = 0,
      lastIndex = -1;
    Cell cCell = first;
    while (cCell != null)
    {
      if (cCell.Data.Equals(dataP))
      {
        lastIndex = index;
      }
      index++;
      cCell = cCell.Next;
    }
    return lastIndex;
  }
 
  // Recursive method to obtain the
  // frequency of dataP
  public double Frequency(T dataP)
  {
    if (Size == 0)
      throw new ArgumentNullException("The list is empty.");
    else
      return Count(dataP, first) / (double)Size;
  }
 
  private int Count(T dataP, Cell pTmp)
  {
    if (pTmp == null)
      return 0;
    else if (pTmp.Data.Equals(dataP))
      return 1 + Count(dataP, pTmp.Next);
    else
      return 0 + Count(dataP, pTmp.Next);
  }
}