// Return a string representing 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);
}
// Return true if the cells after this one form a palindrome.
public bool IsListPalindrome()
{
// Check each cell for a palindrome.
for (LetterCell cell = this.Next; cell != null; cell = cell.Next)
{
if (IsPalindromeAtCell(cell))
{
return(true);
}
}
return(false);
}
// See if the string is a palindrome.
private void checkButton_Click(object sender, EventArgs e)
{
// Make the string into a list.
string txt = stringTextBox.Text.ToUpper();
txt = RemoveNonLetters(txt);
LetterCell sentinel = new LetterCell(txt);
// Check for a palindrome in various ways.
if (sentinel.IsListPalindrome())
{
atCellLabel.Text = "Is a palindrome";
}
else
{
atCellLabel.Text = "Not a palindrome";
}
}
// Return true if the cells before and after this
// one form a palindrome of odd length.
public bool IsEvenPalindromeAtCell(LetterCell cell)
{
// Go forward and backward comparing letters.
LetterCell NextCell = cell;
LetterCell PrevCell = cell;
while ((NextCell != null) && (PrevCell != null))
{
if (NextCell.Letter != PrevCell.Letter)
{
return(false);
}
NextCell = NextCell.Next;
PrevCell = PrevCell.Prev;
}
if ((NextCell != null) || (PrevCell != null))
{
return(false);
}
return(true);
}
// Make a list to represent a string.
public LetterCell(string txt)
{
// Create the end sentinel.
LetterCell endSentinel = new LetterCell();
// Make it into a list.
LetterCell firstCell = endSentinel;
foreach (char ch in txt)
{
LetterCell cell = new LetterCell();
cell.Letter = ch;
cell.Next = firstCell;
firstCell.Prev = cell;
firstCell = cell;
}
// Make this cell be the sentinel.
Next = firstCell;
firstCell.Prev = this;
}
// Return true if the cells before and after this one form a palindrome.
public bool IsPalindromeAtCell(LetterCell cell)
{
return
(IsEvenPalindromeAtCell(cell) ||
IsOddPalindromeAtCell(cell));
}
// Parameterless constructor.
public LetterCell()
{
Letter = '\0';
Next = null;
Prev = null;
}