題目：
最長回文子串：給定一個字符串 s，找到 s 中最長的回文子串。你可以假設 s 的最大長度為 1000。
思路：
思路較簡單，需要考慮回文是奇數還是偶數的情況，但是小坑多，得一一調。
程序：
class Solution:
def longestPalindrome(self, s: str) -> str:
if not s:
return s
length = len(s)
if length == 1:
return s
if length > 1000:
return null
result = ''
auxiliary = 0
for index in range(1, length):
index1 = index - 1
index2 = index
while index1 >= 0 and index2 < length and s[index1] == s[index2]:
index1 -= 1
index2 += 1
if index2 - index1 + 1 > auxiliary:
auxiliary = index2 - index1 + 1
result = s[index1 + 1: index2]
index3 = index - 1
index4 = index + 1
while index3 >= 0 and index4 < length and s[index3] == s[index4]:
index3 -= 1
index4 += 1
if index4 - index3 + 1 > auxiliary:
auxiliary = index4 - index3 + 1
result = s[index3 + 1: index4]
return result