public static string Solution2(string str)
{
Console.WriteLine(str);
if (string.IsNullOrEmpty(str))
{
return(str);
}
var s2 = AddBoundaries(str);
var palindromes = new Palindrome[s2.Length];
var current = new Palindrome(0, 0);
for (var i = 0; i < s2.Length; i++)
{
var min = current.Right > i
? Math.Min(current.Right - i, palindromes[current.GetMirrorCenter(i)].Length)
: 0;
palindromes[i] = new Palindrome(i, min);
current = palindromes[i];
while (current.Left - 1 >= 0 &&
current.Right + 1 < s2.Length &&
s2[current.Left - 1] == s2[current.Right + 1])
{
current.Expand();
}
}
var largest = palindromes.OrderByDescending(p => p.Length).First();
return(RemoveBoundaries(s2.Substring(largest.Left, largest.TotalLength)));
}