查找字符串最长回文
Longest Palindromic Substring
Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.
Example:
Input: "babad"
Output: "bab"
Note: “aba” is also a valid answer.
Example:
Input: "cbbd"
Output: "bb"
思路
回文有奇回文和偶回文,
abcba
是奇回文,abccba
是偶回文回文都是中心对称,找到对称点后,同时向前后寻找回文的最长串即可
奇回文和偶回文可以归为同一种情况,即
abcba
以c
为对称点,abccba
以cc
为对称点,但为了代码可读性,可以分开讨论
代码
class Solution(object):
def longestPalindrome(self, s):
"""
:type s: str
:rtype: str
"""
self.maxlen = 0
self.retstr = ''
if len(s) < 2:
return s
for i in range(len(s)):
self.__find_palindrome(s, i, i) #奇回文
self.__find_palindrome(s, i, i+1) #偶回文
return self.retstr
def __find_palindrome(self, s, j, k):
while j >= 0 and k < len(s) and s[j] == s[k]:
j -= 1
k += 1
if self.maxlen < k - j + 1:
self.maxlen = k - j + 1
self.retstr = s[j+1:k]
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