LeetCode Problem 5

solution.cs

public string LongestPalindrome(string s)
{
    if (s.Length == 0 || s.Length==1)
        return s;

    var longestPali = s[0].ToString();

    for (var i = 0; i < s.Length; i++)
    {
        //Walk backward until you find the same character then start looking for a palindrome
        for (var j = s.Length - 1; j >= i; j--)
        {
            if (s[i] == s[j]) //Potential Palindrome
            {

                var len = j - i+1;

                //If the length is smaller than our current one, why bother!
                if (len <= longestPali.Length)
                    continue;

                var isPalindrome = true;
                var tempPali = new char[len];

                for (int front = i, back = j, first = 0, last = len-1; front <= back; front++, back--, first++, last--)
                {
                    if (s[front] != s[back])
                    {
                        isPalindrome = false;
                        break;
                    }

                    tempPali[first] = s[front];
                    tempPali[last] = s[back];
                }

                var newPali = new string(tempPali);
                if (isPalindrome && newPali.Length > longestPali.Length)
                {
                    longestPali = newPali;
                }

            }
        }

    }

    return longestPali;
}

tests1.cs

[Test]
public void PalindromeInTheBeginning()
{
    _sut.LongestPalindrome("babad").ShouldBe("bab");
}

[Test]
public void PalindromeInTheMiddle()
{
    _sut.LongestPalindrome("cbbd").ShouldBe("bb");
}

[Test]
public void PalindromeAtTheEnd()
{
    _sut.LongestPalindrome("asedad").ShouldBe("dad");
}

tests2.cs

[Test]
public void PalindromeIsTheWholeString()
{
    _sut.LongestPalindrome("racecar").ShouldBe("racecar");
}

[Test]
public void NoPalindromes()
{
    _sut.LongestPalindrome("ab").ShouldBe("a");
}