leetcode:最长回文串-python3

最新推荐文章于 2025-12-16 10:44:31 发布

原创最新推荐文章于 2025-12-16 10:44:31 发布 · 216 阅读

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#python #leetcode #最长字符串

本文介绍了两种寻找字符串中最长回文子串的方法：穷举法和动态规划法。通过详细的代码实现，展示了如何判断一个字符串是否为回文，并找出最长的回文子串。

一、穷举法

class Solution:
    def longestPalindrome(self, s: str) -> str:
        max_len = 0
        s_len = len(s)
        if(s_len <= 1):
            return s
        for i in range(s_len):
            for j in range(i,s_len):
                s_1 = s[i:j+1]
                if(len(s_1) >= max_len and isPalindromic(s_1)):
                    rs = s_1
                    max_len = len(s_1)
        return rs
    
def isPalindromic(s_1:str) -> bool:
    s_2 = s_1[::-1]
    if(s_1 == s_2):
        return True
    return False

二、动态规划

class Solution:
    def longestPalindrome(self, s: str) -> str:
        
        
        s_len = len(s)
        
        if(s_len == 0 or s_len == 1):
            return s
        
        p = [[0] * s_len for i in range(s_len)]
        
        max_len = 0
        for i in range(1,s_len+1):
            for start in range(s_len):
                end = i + start - 1
                if end >= s_len:
                    break
                if(i==1):
                    p[start][end] = True
                    max_s = s[start:end+1]
                    continue
                if(i==2 and s[start]==s[end]):
                    p[start][end] = True
                    max_s = s[start:end+1]
                    continue
                p[start][end]=(p[start+1][end-1] and s[start]==s[end])
                
                
                if(p[start][end] and i > max_len):
                    max_s = s[start:end+1]
                    
        return max_s