longestPalindrome.py

class Solution(object):
    def longestPalindrome(self, s):
        """
        :type s: str
        :rtype: str
        """
        def check_palindrom(start, end):
            while start > 0 and end < n-1 and s[start-1] == s[end+1]:
                start-=1
                end+=1
            length = end - start + 1
            if length > longest[2]:
                longest[0] = start
                longest[1] = end
                longest[2] = length

        # if no palindrom is found return the first character
        # longest is [start, end, length]
        longest = [0,0,1]
        n = len(s)

        # edge cases
        if n == 1:
            return s[0]
        if n == 2:
            if s[0] == s[1]:
                return s
            else:
                return s[0]

        for i in range(0, n-1):
            if s[i] == s[i+1]:
                longestPossible = 2 * min(n-i-1, i+1)
                if longestPossible > longest[2]:
                    check_palindrom(i, i+1)

            if i > 0 and s[i-1] == s[i+1]:
                longestPossible = 2 * min(n-i, i+1) - 1
                if longestPossible > longest[2]:
                    check_palindrom(i-1, i+1)

        return s[longest[0]:longest[1]+1]