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"
题意：找到一个字符串的最长回文子串
思路：枚举中心位置，向两边扩展，并及时更新最长回文字串。此处回文长度是奇数和偶数分开处理。
1 class Solution: 2 def longestPalindrome(self,s): 3 n = len(s) 4 a = ‘‘ 5 if n < 1: 6 return 0 7 max = 0 8 for i in range(n): #i记录回文串的中心 9 j = 0 10 while (i-j >= 0) and (i+j < n): #回文串长度为奇数 11 if s[i-j] != s[i+j]: 12 break 13 c = j*2+1 14 j += 1 15 if c > max: 16 max = c 17 a = s[i-j+1:i+j] 18 k = 0 19 while (i - k >= 0) and (i + k + 1 < n): #回文串长度为偶数 20 if s[i-k] != s[i+k+1]: 21 break 22 c = k*2+2 23 k += 1 24 if c > max: 25 max = c 26 a = s[i - k + 1 : i + k + 1] 27 return a 28 29 if __name__==‘__main__‘: 30 solution=Solution() 31 print(solution.longestPalindrome(‘abaab‘))