LeetCode Longest Palindromic Substring

Input: "babad"
Output: "bab"
Note: "aba" is also a valid answer.

Input: "cbbd"
Output: "bb"

class Solution:
    def longestPalindrome(self, s):
        """
        :type s: str
        :rtype: str
        """
        n=len(s)
        if n==1 or n==0:
            return s
        if n==2:
            if s[0]==s[1]:
                return s
            else:
                return s[0]
        max_length=1
        ans=s[0]
        i=0
        while i<n:
            j=i+1
            while j<n:
                if s[i]==s[j]:
                    j+=1
                else:
                    break
            k=0
            while i-k-1>=0 and j+k<=n-1:
                if s[i-k-1]!=s[j+k]:
                    break
                k+=1
            if j-i+2*k>max_length:
                max_length=j-i+2*k
                ans=s[i-k:j+k]
            # if j+k==n-1:
            #    break
            i=j
        return ans

class Solution:
    def longestPalindrome(self, s):
        if s == s[::-1]:
            return s
        Len, start  = 1, 0
        for i in range(1, len(s)):
            c, d = i - Len, i + 1
            if c >= 1:
                x = s[c - 1:d]
                if x == x[::-1]:
                    start = c - 1
                    Len += 2
                    continue
            if c >= 0:
                x = s[c:d]
                if x == x[::-1]:
                    start = c
                    Len += 1
        return s[start:start + Len]