leetcode第五题答案

中心扩散，如果两边的字母相同，就可以继续扩展；如果两边的字母不同，就停止扩展

class Solution(object):

"""调用此处提供下标"""

def xh(self,s,i,j):

while i>=0 and j<len(s) and s[i] == s[j]:

i -= 1

j +=1

return i+1,j-1

"""遍历奇偶，找最长"""

def longestPalindrome(self, s):

"""

:type s: str

:rtype: str

"""

start = 0

end = 0

m = len(s)

i = 0

for i in range(m):

s1,e1 = self.xh(s,i,i)

s2,e2 = self.xh(s,i,i+1)

if e1 - s1 > end - start:

end = e1

start = s1

if e2 - s2 > end -start:

end = e2

start = s2

return s[start:end+1]