// Return the first cell in the second half of the list.
// If the list has an odd number of cells and
// countMiddleCell is true, return the middle cell.
// If the list has an odd number of cells and
// countMiddleCell is false, return the cell after the middle.
public LetterCell FindSecondHalf(bool countMiddleCell)
{
// Find the list's halfway point.
LetterCell slowCell = this;
LetterCell fastCell = slowCell;
for (; ;)
{
// Move slowCell.
slowCell = slowCell.Next;
// Move fastCell.
fastCell = fastCell.Next;
if (fastCell == null)
{
// The list has an even number of items and
// slowCell is the first cell in the second half.
return(slowCell);
}
fastCell = fastCell.Next;
if (fastCell == null)
{
// The list has an odd number of items
// and slowCell is the middle item.
if (!countMiddleCell)
{
slowCell = slowCell.Next;
}
return(slowCell);
}
}
}
// Display the second halves of the text.
private void goButton_Click(object sender, EventArgs e)
{
halfWoMiddleTextBox.Clear();
halfWithMiddleTextBox.Clear();
// Make the list.
LetterCell sentinel = new LetterCell(stringTextBox.Text);
if (sentinel.Next == null)
{
return;
}
// Get the second halves.
LetterCell half;
half = sentinel.FindSecondHalf(false);
if (half != null)
{
halfWoMiddleTextBox.Text = half.ToString();
}
half = sentinel.FindSecondHalf(true);
if (half != null)
{
halfWithMiddleTextBox.Text = half.ToString();
}
}
// Return the text in this cell and those that follow.
public override string ToString()
{
string result = "";
for (LetterCell cell = this; cell != null; cell = cell.Next)
{
result += cell.Letter;
}
return(result);
}
// Make a list from a string.
public LetterCell(string txt)
{
// Add each letter to the end.
this.Next = null;
LetterCell lastCell = this;
foreach (char ch in txt)
{
LetterCell newCell = new LetterCell();
newCell.Letter = ch;
newCell.Next = null;
lastCell.Next = newCell;
lastCell = newCell;
}
}
