/// <summary>
/// Gets the longest Palindrome from the string.
/// </summary>
/// <param name="input">The input string.</param>
/// <returns>The resulting palindrome.</returns>
public static string FindLongestPalindrome(string input)
{
// Error handling.
if (input == null)
{
throw new ArgumentException();
}
// Check strings of length input, then strings of length - 1, length - 2 etc.
for (var len = input.Length; len > 0; len--)
{
for (var startindex = 0; startindex < len - startindex; startindex++)
{
// Get the string & see if it is a palindrome.
var toCheck = input.Substring(startindex, len - startindex);
if (IsPalindrome1StandardComplete.IsPalindrome(toCheck))
{
return(toCheck);
}
}
}
// No palindrome found.
return(string.Empty);
}
/// <summary>
/// Finds Palindrome permutations.
/// Note that the input string must be a Palindrome.
/// </summary>
/// <param name="input">The input string.</param>
/// <returns>The resulting palindrome permutations.</returns>
public static List <string> FindPalindromePermutations(string input)
{
// Error Checking.
if (input == null)
{
throw new ArgumentException("Input string must be non-null.");
}
if (!IsPalindrome1StandardComplete.IsPalindrome(input))
{
throw new ArgumentException("Input string must be a palindrome.");
}
// Initialize result.
var result = new List <string>();
// No other results if less than 4.
if (input.Length < 4)
{
// String itself is a palindrome.
result.Add(input);
return(result);
}
// Split the string.
var halflen = input.Length / 2;
var left = input.Substring(0, halflen);
// Get permutations for first half of string.
var permutations = GetPermutations2UseDictionaryComplete.GetPermutations(left);
// Build resulting strings.
foreach (var permutation in permutations)
{
// Reverse the permutation.
var permutationReversed = string.Concat(permutation.Reverse());
// Add resulting string.
result.Add(permutation + (input.Length % 2 == 1 ? input[halflen].ToString() : string.Empty) + permutationReversed);
}
// Return result.
return(result);
}
