5. 最长回文子串python

回答: 最长回文子串可以通过两种方法来实现。第一种是使用中心扩展法，代码如下：

class Solution:
    def check(self, s, l, r):
        while l >= 0 and r < len(s) and s[l == s[r]:
            l -= 1
            r += 1
        return l + 1, r - 1

    def longestPalindrome(self, s: str) -> str:
        start, end = 0, 0
        for x in range(len(s)):
            l1, r1 = self.check(s, x, x)
            l2, r2 = self.check(s, x, x + 1)
            if r1 - l1 > end - start:
                start, end = l1, r1
            if r2 - l2 > end - start:
                start, end = l2, r2
        return s[start:end+1]

第二种方法是使用动态规划，代码如下：

class Solution:
    def longestPalindrome(self, s: str) -> str:
        res = ''
        for i in range(len(s)):
            start = max(0, i - len(res) - 1)
            temp = s[start:i+1]
            if temp == temp[::-1]:
                res = temp
            else:
                temp = temp<span class="em">1</span><span class="em">2</span><span class="em">3</span>
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