文字列sが与えられた場合、sで最長のpalindromeサブ文字列を見つけます。sの最大長は1000であると想定できます。
例1:
入力: "babad"
出力: "bab"
注: "aba"も有効な答えです。ソース:LeetCode
リンク:https ://leetcode-cn.com/problems/longest-palindromic-substring
方法1:動的プログラミング方法
class Solution:
def longestPalindrome(self, s: str) -> str:
length=len(s)
if length<=1: return s
dp=[[ False for _ in s ]for _ in s]
start=0
max_len=1
for j in range(1,length):
for i in range(0,j):
if j-i<3:
dp[i][j]= s[i]==s[j]
else:
dp[i][j]= s[i]==s[j] and dp[i+1][j-1]
if dp[i][j]:
cur_len=j-i+1
if cur_len>max_len:
max_len=cur_len
start=i
return s[start:start+max_len]
方法2:
class Solution:
def longestPalindrome(self, s: str) -> str:
maxlen = 0
start = 0
if not s or s == "":
return ""
if s == s[::-1] or len(s) == 1:
return s
for i in range(1,len(s)):
odd = s[i - maxlen - 1:i + 1]
even = s[i - maxlen:i + 1]
if odd == odd[::-1] and i - maxlen - 1 >= 0:
start = i - maxlen - 1
maxlen += 2
elif even == even[::-1] and i- maxlen - 1 >= 0:
start = i - maxlen
maxlen += 1
return s[start:start+maxlen]
ps: