1.最長迴文子串
題目連結：https://leetcode.cn/problems/longest-palindromic-substringm/
給定一個字串 s，找到 s 中最長的 迴文 子串
class Solution:
def longestPalindrome(self, s: str) -> str:
def expand_around_center(left, right):
while left >= 0 and right < len(s) and s[left] == s[right]:
left -= 1
right += 1
return s[left + 1:right]
res = ""
for i in range(len(s)):
palindrome1 = expand_around_center(i, i)
palindrome2 = expand_around_center(i, i + 1)
if len(palindrome1) > len(res):
res = palindrome1
if len(palindrome2) > len(res):
res = palindrome2
return res
2.Z 字形變換
題目連結：https://leetcode.cn/problems/zigzag-conversion/
將一個給定字串 s 根據給定的行數 numRows ，以從上往下、從左到右進行 Z 字形排列。
class Solution:
def convert(self, s: str, numRows: int) -> str:
if numRows == 1 or numRows >= len(s):
return s
rows = ['' for _ in range(numRows)]
index, step = 0, 1
for char in s:
rows[index] += char
if index == 0:
step = 1
elif index == numRows - 1:
step = -1
index += step
return ''.join(rows)